Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : A pure semiconductor has negative temperature coefficient of resistance. Reason : In a semiconductor on raising the temperature, more charge carriers are released, conductance increases and resistance decreases.
Answer(a) In semiconductors, by increasing temperature, covalent bond breaks and conduction hole and electrons increase.
Q.2. Assertion : If the temperature of a semiconductor is increased then its resistance decreases. Reason : The energy gap between conduction band and valence band is very small.
Answer(a) In semiconductors the energy gap between conduction band and valence band is small (1 eV). Due to temperature rise, electron in the valence band gain thermal energy and may jumpy across the small energy gap, (to the conduction band). Thus conductivity increases and hence resistance decreases.
Q.3. Assertion : In semiconductors, thermal collisions are responsible for taking a valence electron to the conduction band. Reason : The number of conduction electrons go on increasing with time as thermal collisions continuously take place.
Answerc
Q.4. Assertion : A p-type semiconductors is a positive type crystal. Reason : A p- type semiconductor is an uncharged crystal.
Answer(d) There is no charge on P-type semiconductor, because each atom of semiconductor is itself neutral.
Q.5. Assertion : Silicon is preferred over germanium for making semiconductor devices. Reason : The energy gap in germanium is more than the energy gap in silicon.
Answer(c) Silicon is cheaper than germanium, so it is preferred over germanium. But energy gap in germanium is smaller than silicon.
Q.6. Assertion : Electron has higher mobility than hole in a semiconductor. Reason : The mass of electron is less than the mass of the hole.
Answer-a
Q.7. Assertion : The number of electrons in a p-type silicon semiconductor is less than the number of electrons in a pure silicon semiconductor at room temperature. Reason : It is due to law of mass action.
Answer-a
Q.8. Assertion : When two semi conductor of p and n type are brought in contact, they form p-n junction which act like a rectifier. Reason : A rectifier is used to convent alternating current into direct current.
Answer(b) Study of junction diode characteristics shows that the junction diode offers a low resistance path, when forward biased and high resistance path when reverse biased. This feature of the junction diode enables it to be used as a rectifier.
Q.9. Assertion : Diode lasers are used as optical sources in optical communication. Reason : Diode lasers consume less energy.
Answer(c) Statement – 1 is True, Statement- 2 is False
Q.10. Assertion : The diffusion current in a p-n junction is from the p-side to the n-side. Reason : The diffusion current in a p-n junction is greater than the drift current when the junction is in forward biased.
Answer(b) Diffusion current is due to the migration of holes and electrons into opposite regions, so it will be from p-side to n-side. Also in forward bias it will increases.
Q.11. Assertion : The drift current in a p-n junction is from the n-side to the p-side. Reason : It is due to free electrons only.
Answer-a
Q.12. Assertion : A p-n junction with reverse bias can be used as a photo-diode to measure light intensity. Reason : In a reverse bias condition the current is small but it is more sensitive to changes in incident light intensity.
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : Density of all the nuclei is same. Reason : Radius of nucleus is directly proportional to the cube root of mass number.
Answer-a
Q.2. Assertion : Neutrons penetrate matter more readily as compared to protons. Reason : Neutrons are slightly more massive than protons.
Answer(b) Both statements are separately correct.
Q.3. Assertion : The mass number of a nucleus is always less than its atomic number. Reason : Mass number of a nucleus may be equal to its atomic number.
Answer(d) In case of hydrogen atom mass number and atomic number are equal.
Q.4. Assertion : The binding energy per nucleon, for nuclei with atomic mass number A > 100, decrease with A. Reason : The forces are weak for heavier nuclei.
Answer(c) Nuclear force is nearly same for all nucleus.
Q.5. Assertion : Radioactivity of 108 undecayed radioactive nuclei of half life of 50 days is equal to that of 1.2 × 108 number of undecayed nuclei of some other material with half life of 60 days. Reason : Radioactivity is proportional to half-life.
Answer-c
Q.6. Assertion : The ionising power of β-particle is less compared to β-particles but their penetrating power is more. Reason : The mass of β-particle is less than the mass of α- particle.
Answer(b) β-particles, being emitted with very high speed compared to α-particles, pass for very little time near the atoms of the medium. So the probability of the atoms being ionised is comparatively less. But due to this reason, their loss of energy is very slow and they can penetrate the medium through a sufficient depth.
Q.8. Assertion : ZXA undergoes 2α, 2β- particles and 2γ-rays, the daughter product is Z-2YA – 8. Reason : In α- decay the mass number decreases by 4 and atomic number decreases by 2. In β-decay the mass number remains unchanged, but atomic number increases by 1.
Answer-a
Q.9. Assertion : The heavier nuclei tend to have larger N/Z ratio because neutron does not exert electric force. Reason : Coulomb forces have longer range compared to the nuclear force.
Answer-a
Q.10. Assertion : A free neutron decays to a proton but a free proton does not decay to a neutron. This is because neutron is an uncharged particle and proton is a charged particle. Reason : Neutron has larger rest mass than the proton.
Answer-d
Q.11. Assertion : Cobalt-60 is useful in cancer therapy. Reason : Cobalt -60 is source of γ- radiations capable of killing cancerous cells.
Answer-d
Q.12. Assertion : It is not possible to use 35Cl as the fuel for fusion energy. Reason : The binding energy of 35Cl is to small.
Answer-c
Q.13. Assertion : Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion. Reason : For heavy nuclei, binding energy per nucleon increases with increasing Z while for light nuclei it decreases with increasing Z.
Answer(d) We know that energy is released when heavy nuclei undergo fission or light nuclei undergo fusion. Therefore statement (1) is correct. The second statement is false because for heavy nuclei the binding energy per nucleon decreases with increasing Z and for light nuclei, B.E/nucleon increases with increasing Z.
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : The force of repulsion between atomic nucleus and α-particle varies with distance according to inverse square law. Reason : Rutherford did α-particle scattering experiment.
Answer(b) Rutherford confirmed that the repulsive force of α- particle due to nucleus varies with distance according to inverse square law and that the positive charges are concentrated at the centre and not distributed throughout the atom.
Q.2. Assertion : According to classical theory the proposed path of an electron in Rutherford atom model will be parabolic. Reason : According to electromagnetic theory an accelerated particle continuously emits radiation.
Answer(d) According to classical electromagnetic theory, an accelerated charged particle continuously emits radiation. As electrons revolving in circular paths are constantly experiencing centripetal acceleration, hence they will be losing their energy continuously and the orbital radius will go on decreasing, form spiral and finally the electron will fall in the nucleus.
Q.3. Assertion : Bohr had to postulate that the electrons in stationary orbits around the nucleus do not radiate. Reason: According to classical physics all moving electrons radiate.
Answer(b) Bohr postulated that electrons in stationary orbits around the nucleus do not radiate. This is the one of Bohr’s postulate, According to this the moving electrons radiates only when they go from one orbit to the next lower orbit.
Q.4. Assertion : Electrons in the atom are held due to coulomb forces. Reason : The atom is stable only because the centripetal force due to Coulomb’s law is balanced by the centrifugal force.
Answer(c) According to postulates of Bohr’s atom model the electron revolves around the nucleus in fixed orbit of definite radii. As long as the electron is in a certain orbit it does not radiate any energy.
Q.5. Assertion : Hydrogen atom consists of only one electron but its emission spectrum has many lines. Reason : Only Lyman series is found in the absorption spectrum of hydrogen atom whereas in the emission spectrum, all the series are found.
Answer(b) When the atom gets appropriate energy from outside, then this electron rises to some higher energy level. Now it can return either directly to the lower energy level or come to the lowest energy level after passing through other lower energy levels hence all possible transitions take place in the source and many lines are seen in the spectrum.
Q.6. Assertion : Between any two given energy levels, the number of absorption transitions is always less than the number of emission transitions. Reason : Absorption transitions start from the lowest energy level only and may end at any higher energy level. But emission transitions may start from any higher energy level and end at any energy level below it.
Answer(a)
Q.7. Assertion : In Lyman series, the ratio of minimum and maximum wavelength is 3/4 Reason : Lyman series constitute spectral lines corresponding to transition from higher energy to ground state of hydrogen atom.
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : In process of photoelectric emission, all emitted electrons do not have same kinetic energy. Reason : If radiation falling on photosensitive surface of a metal consists of different wavelength then energy acquired by electrons absorbing photons of different wavelengths shall be different.
Answer(b) Both statement I and II are true; but even it radiation of single wavelength is incident on photosensitive surface, electrons of different KE will be emitted.
Q.2. Assertion : Though light of a single frequency (monochromatic) is incident on a metal, the energies of emitted photoelectrons are different. Reason : The energy of electrons emitted from inside the metal surface, is lost in collision with the other atoms in the metal.
Answer(a) When a light of single frequency falls on the electrons of inner layer of metal, then this electron comes out of the metal surface after a large number of collisions with atom of it’s upper layer.
Q.3. Assertion : The photoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies. Reason : The work function of the metal is its characteristics property.
Answer(b) The kinetic energy of emitted photoelectrons varies from zero to a maximum value. Work function depends on metal used.
Q.4. Assertion : Photoelectric saturation current increases with the increase in frequency of incident light. Reason : Energy of incident photons increases with increase in frequency and as a result photoelectric current increases.
Answer(d) Photoelectric saturation current is independent of frequency. It only depends on intensity of light.
Q.5. Assertion : Photosensitivity of a metal is high if its work function is small. Reason : Work function = hf0 where f0 is the threshold frequency.
Answer(b) Less work function means less energy is required for ejecting out the electrons.
Q.6. Assertion : The photon behaves like a particle. Reason : If E and P are the energy and momentum of the photon, then p = E / c .
Answer-a
Q.7. Assertion : In an experiment on photoelectric effect, a photon is incident on an electron from one direction and the photoelectron is emitted almost in the opposite direction. It violate the principle of conservation of linear momentum. Reason : It does not violate the principle of conservation of linear momentum.Answerd
Q.9. Assertion : Two sources of equal intensity always emit equal number of photons in any time interval. Reason : Two sources of equal intensity may emit equal number of photons in any time interval.
Answer(d) Total number of emitted photons depends on energy of each photon. The energy of photons of two sources may be different.
Q.10. Assertion : Two photons of equal wavelength must have equal linear momentum. Reason : Two photons of equal linear momentum will have equal wavelength.
Answer(d) To photons of equal wavelength will have equal momentum (magnitude), but direction of momentum may be different.
Q.11. Assertion : The kinetic energy of photoelectrons emitted from metal surface does not depend on the intensity of incident photon. Reason : The ejection of electrons from metallic surface is not possible with frequency of incident photons below the threshold frequency.
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : According to Huygen’s principle, no backward wave-front is possible. Reason : Amplitude of secondary wavelet is proportional to (1 + cos θ) where θ is the angle between the ray at the point of consideration and the direction of secondary wavelet.Answerb
Q.2. Assertion : Thin film such as soap bubble or a thin layer of oil on water show beautiful colours when illuminated by white light. Reason : It happens due to the interference of light reflected from upper and lower face of the thin film.Answer
Q.3. Assertion : No interference pattern is detected when two coherent sources are infinitely close to each other. Reason : The fringe width is inversely proportional to the distance between the two sources.Answera
Q.4. Assertion : It is necessary to have two waves of equal intensity to study interference pattern. Reason : There will be an effect on clarity if the waves are of unequal intensity.Answer(d) For interference, the waves may be of unequal intensities.
Q.5. Assertion : White light falls on a double slit with one slit is covered by a green filter. The bright fringes observed are of green colour. Reason : The fringes observed are coloured.Answer(c) Interference will take place in green light only
Q.6. Assertion : In YDSE, if a thin film is introduced in front of the upper slit, then the fringe pattern shifts in the downward direction. Reason : In YDSE if the slit widths are unequal, the minima will be completely dark.Answerd
Q.7. Assertion : In Young’s double slit experiment if wavelength of incident monochromatic light is just doubled, number of bright fringe on the screen will increase. Reason : Maximum number of bright fringe on the screen is inversely proportional to the wavelength of light usedAnswera
Q.8. Assertion : In YDSE number of bright fringe or dark fringe can not be unlimited Reason : In YDSE path difference between the superposing waves can not be more than the distance between the slits.Answerb
Q.9. Assertion : Interference pattern is made by using yellow light instead of red light, the fringes becomes narrower. Reason : In YDSE, fringe width is given by β=λD/dAnswera
Q.10. Assertion : Coloured spectrum is seen when we look through a muslin cloth. Reason : It is due the diffraction of white light on passing through fine slits.Answera
Q.11. Assertion : Diffraction takes place for all types of waves mechanical or non-mechanical, transverse or longitudinal. Reason : Diffraction’s effect are perceptible only if wavelength of wave is comparable to dimensions of diffracting device.Answerb
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : Plane mirror may form real image. Reason : Plane mirror forms virtual image, if object is real.
Answer-b
Q.2. Assertion : The focal length of the convex mirror will increase, if the mirror is placed in water. Reason : The focal length of a convex mirror of radius R is equal to , f = R/2.
Answer(d) Focal length of the spherical mirror does not depend on the medium in which it placed.
Q.3. Assertion : The image formed by a concave mirror is certainly real if the object is virtual. Reason : The image formed by a concave mirror is certainly virtual if the object is real.
Answer(c) The image of real object may be real in case of concave mirror.
Q.4. Assertion : The image of an extended object placed perpendicular to the principal axis of a mirror, will be erect if the object is real but the image is virtual. Reason : The image of an extended object, placed perpendicular to the principal axis of a mirror, will be erect if the object is virtual but the image is real.
Answer-b
Q.5. Assertion : An object is placed at a distance of f from a convex mirror of focal length f its image will form at infinity. Reason : The distance of image in convex mirror can never be infinity
Answer-d
Q.6. Assertion : The image of a point object situated at the centre of hemispherical lens is also at the centre. Reason : For hemisphere Snell’s law is not valid.
Answer(c) The rays from centre of hemisphere cut at the centre after refraction – Snell’s law is valid in each case of refraction.
Q.7. Assertion: The focal length of an equiconvex lens of radius of curvature R made of material of refractive index μ = 1.5, is R. Reason : The focal length of the lens will be R/2.
Answer(c)
Q.8. Assertion : If the rays are diverging after emerging from a lens; the lens must be concave. Reason : The convex lens can give diverging rays.
Answer(d) If the rays cross focal point of convex lens, they become diverging.
Q.9. Assertion : The resolving power of a telescope is more if the diameter of the objective lens is more. Reason : Objective lens of large diameter collects more light.
Answer(a) RP α diameter of objective.
Q.10. Assertion : The optical instruments are used to increase the size of the image of the object. Reason : The optical instruments are used to increase the visual angle.
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : Electromagnetic wave are transverse in nature. Reason : The electric and magnetic fields in electromagnetic waves are perpendicular to each other and the direction of propagation.
Answer(a) Transverse waves are those waves in which the particles of the medium oscillate perpendicular to the direction of wave propagation.
Q.2. Assertion : Electromagnetic waves interact with matter and set up oscillations. Reason : Interaction is independent of the wavelength of the electromagnetic wave.
Answer(c) Electromagnetic waves interact with matter via their electric and magnetic field which in oscillation of charges present in all matter. The detailed interaction and so the mechanism of absorption, scattering, etc. depend of the wavelength of the electromagnetic wave, and the nature of the atoms and molecules in the medium.
Q.3. Assertion : Electromagnetic waves carry energy and momentum. Reason : Electromagnetic waves can be polarised.
Answer(b) Consider a plane perpendicular to the direction of propagation of the electromagnetic wave. If electric charges are present in this plane, they will be set and sustained in motion by the electric and magnetic fields of the electromagnetic wave. The charge thus acquired energy and momentum from the wave. This illustrate the fact that an electromagnetic wave like other waves carries energy and momentum.
Answer(a) Electromagnetic waves have linear momentum as well as energy. This concludes that they can exert radiation pressure by falling beam of electromagnetic radiation on an object.
Q.5. Assertion : The electromagnetic wave is transverse in nature. Reason : Electromagnetic wave propagates parallel to the direction of electric and magnetic fields.
Answer(c) This electromagnetic wave contains sinusoidally time varying electric and magnetic field which act perpendicular to each other as well as at right angle to the direction of propagation of waves, so electromagnetic waves are transverse in nature. Electromagnetic wave propagate in the perpendicular direction to both fields.
Q.6. Assertion : The velocity of electromagnetic waves depends on electric and magnetic properties of the medium. Reason : Velocity of electromagnetic waves in free space is constant.
Answer(b)
Q.7. Assertion : The basic difference between various types of electromagnetic waves lies in their wavelength or frequencies. Reason : Electromagnetic waves travel through vacuum with the same speed.
Answer(a) The basic difference between various types of electromagnetic waves lies in their wavelengths or frequencies since all of them travel through vacuum with the same speed. Consequently, the waves differ considerably in their mode of interaction with matter.
Q.8. Assertion : Microwaves are better carrier of signals than optical waves. Reason : Microwaves move faster than optical waves.
Answer(d) The optical waves used in optical fibre communication are better carrier of signals than microwaves. The speed of microwave and optical wave is the same in vacuum.
Q.9. Assertion : Infrared radiation plays an important role in maintaining the average temperature of earth. Reason : Infrared radiations are sometimes referred to as heat waves
Answer(b) Infrared radiation help to maintain the earth warmth through the greenhouse effect. Incoming visible light which passes relatively easily through the atmosphere is absorbed by the earth’s surface and re-radiated as infrared radiation. The radiation is trapped by greenhouse gases such as carbon dioxide and water vapour and they heat up and heat their surroundings
Both assertion and reason are true and reason is the correct explanation of assertion.
Both assertion and reason are true but reason is not the correct explanation of assertion.
Assertion is true but reason is false.
Assertion is false but reason is true.
1. Assertion AC is more dangerous in use than DC
Reason It is because the peak value of AC is greater than indicated value
2. Assertion Average value of AC over a complete cycle is always zero
Reason average value of AC is always defined over half cycle
3. Assertion The alternating current lags behind the EMF by a phase angle of when AC flows through and inductor
Reason The inductive reactance increases as the frequency of AC source decreases
4. Assertion Capacitor serves as a block for DC and offers an easy path to AC
Reason Capacitive reactance is inversely proportional to frequency
5. Assertion In series LCR resonant circuit the impedance is equal to the ohmic resistance
Reason At resonance the inductive reactance exceeds the capacitive reactance
6. Assertion An alternating current shows magnetic effect
Reason Alternating current varies with time
7. Assertion In series LCR circuit resonance can take place
Reason Resonance takes place in inductance and capacitive reactance are equal and opposite
8. Assertion Power factor correction is must in heavy machinery
Reason A low power factor implies larger power loss in transmission
9. Assertion Choke coil is preferred over a registered to adjust current in an AC circuit
Reason Power factor for inductance is zero
10. Assertion When AC circuit containing resistor only its power is minimum
Reason Power of a circuit is independent of phase angle
11. Assertion A transformer cannot work on DC supply
Reason DC change is neither in magnitude nor in direction
12. Assertion A laminated core is used in transformer to increase eddy currents
Reason The efficiency of a transformer increases with increase in eddy currents
13. Assertion Soft iron is used as a core of transformer
Reason Area of hysteresis loop for soft iron is small
14. Assertion An AC generator is based on the phenomenon of electromagnetic induction
Reason In single coil we consider self induction only
Assertion-Reasoning Based MCQAnswers
1. (1)
AC is more dangerous in use than DC. It is because the peak value of AC is greater than the indicated value.
2. (2)
The mean or average value of alternating current or EMF during half cycle is given by
Im = 0.636 Io Em = 0.6363 Eo
During the next half cycle, the mean value of AC will be equal in magnitude but opposite in direction. For this reason the average value of AC over a complete cycle is always zero. So the average value is always defined over a half cycle of AC.
3. (3)
When AC flows through an inductor current lags behind the EMF, by phase of π/2 inductive reactance
XL = ωL = 2πfL
So, when frequency increases correspondingly inductive reactance also increases.
4. (1)
The capacitive reactance of capacitor is given by
XC = 1/ ωC = 1/2πfC
So this is infinite for DC and has a very small value for AC. Hence, a capacitor blocks DC.
5. (3)
In series resonance circuit inductive reactance is equal to capacitive reactance.
ωL = 1/ωC
Z = R
6. (2)
Like direct current, an AC also produces magnetic field. But the magnitude and direction of the field goes on changing continuously with time.
7. (1)
At resonant frequency,
XL = XC, Z = R (minimum)
8. (2)
A heavy machinery requires a large power.
The average power is given by,
Pav = ErmsIrmscosΦ
The required power can be supplied to the heavy machinery either by supplying larger current or by improving power factor. The first method is costly. Hence, the second one is used.
9. (1)
We can use a capacitor of suitable capacitance as a choke coil, because average power consumed per cycle in an ideal capacitor is zero. Therefore, like a choke coil a condenser can reduce AC without power dissipation.
10. (4)
The power of an AC circuit is given by,
P = EIcosΦ
Where cosΦ is a power factor and is Φ phase angle. In case of circuit containing resistance only, phase angle is zero and power factor is equal to 1. Therefore power is maximum in case of circuit containing resistor only.
11. (1)
Transformer works on AC only AC changes in magnitude as well as in direction and induced EMF.
12. (4)
Large eddy currents are produced in non laminated iron core of the transformer by induced EMF, as the resistance of bulk iron core is very small. By using thin iron sheets are score the resistance is increased. Laminating the core substantially reduces the eddy currents. Eddy currents heat up the core of the transformer. More the eddy current greater the loss of energy and efficiency goes down.
13. (1)
Hysteresis loss in the core of transformer is directly proportional to the hysteresis loop area of the core material. Since soft iron has narrow hysteresis loop area, that is why soft iron core is used in transformer.
14. (2)
According to electromagnetic induction, whenever the magnetic flux changes and EMF will be induced in the coil.
Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect.
Q.1. Assertion : Induced emf will always occur whenever there is change in magnetic flux. Reason : Current always induces whenever there is change in magnetic flux.
Answer(c) Emf will always induces whenever, there is change in magnetic flux. The current will induced only in closed loop.
Q.2. Assertion : Faraday’s laws are consequence of conservation of energy. Reason : In a purely resistive ac circuit, the current legs behind the emf in phase.
Answer(c) In purely resistive circuit, the current and emf are in the same phase.
Q.3. Assertion : Only a change in magnetic flux will maintain an induced current in the coil. Reason : The presence of large magnetic flux through a coil maintain a current in the coil of the circuit is continuous.
Answer(c)
Q.4. Assertion : Lenz’s law violates the principle of conservation of energy. Reason : Induced emf always opposes the change in magnetic flux responsible for its production.
Answer(a) Lenz’s law (that the direction of induced emf is always such as to oppose the change that cause it) is direct consequence of the law of conservation of energy.
Q.5. Assertion : An induced current has a direction such that the magnetic field due to the current opposes the change in the magnetic flux that induces the current. Reason : Above statement is in accordance with conservation of energy.
Answer(b)
Q.6. Assertion : Acceleration of a magnet falling through a long solenoid decreases. Reason : The induced current produced in a circuit always flow in such direction that it opposes the change to the cause that produced it.
Answer(a)
Q.7. Assertion : Figure shows a horizontal solenoid connected to a battery and a switch. A copper ring is placed on a smooth surface, the axis of the ring being horizontal. As the switch is closed, the ring will move away from the solenoid.
Reason : Induced emf in the ring, e=-dΦ/dt
Answer(a)When switch is closed , the magnetic flux through the ring will increase and so ring will move away form the solenoid so as to compensate this flux. This is according to Lenz’s law.
Q.8. Assertion : An emf can be induced by moving a conductor in a magnetic field. Reason : An emf can be induced by changing the magnetic field.
Answer(b) In both the cases, the magnetic flux will change, and so there is an induced current.
Q.9. Assertion : Figure shows a metallic conductor moving in magnetic field. The induced emf across its ends is zero.
Reason : The induced emf across the ends of a conductor is given by e = Bvℓ sinθ.
Answer(a)
Q.10. Assertion : Eddy currents are produced in any metallic conductor when magnetic flux is changed around it. Reason : Electric potential determines the flow of charge.
Answer(b) Both the statements are independently correct.
Q.11. Assertion : An induced emf appears in any coil in which the current is changing. Reason : Self induction phenomenon obeys Faraday’s law of induction.
Answer(b)
Q.12. Assertion : When number of turns in a coil is doubled, coefficient of self-inductance of the coil becomes 4 times. Reason : This is because L α N2.
