# Physics MCQs for Class 12 with Answers Chapter 3 Current Electricity

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#### MCQs based on Current Electricity:

Q.1. In a current carrying conductor the net charge is
(a) 1.6 x 10–19 coulomb
(b) 6.25 x 10–18 coulomb
(c) zero
(d) infinite

(c)
Explanation:
In a current carrying conductor, the net charge is zero.

Q.2. The current which is assumed to be flowing in a circuit from positive terminal to negative, is called
(a) direct current
(b) pulsating current
(c) conventional current
(d) alternating current

(c)

Q.3. When no current is passed through a conductor,
(a) the free electrons do not move
(b) the average speed of a free electron over a large period of time is not zero
(c) the average velocity of a free electron over a large period of time is zero
(d) the average of the velocities of all the free electrons at an instant is non zero

(d)

Q.4. A current passes through a wire of nonuniform cross-section. Which of the following quantities are independent of the cross-section?
(a) The charge crossing
(b) Drift velocity
(c) Current density
(d) Free-electron density

(d)

Q.5. In the equation AB = C, A is the current density, C is the electric field, Then B is
(a) resistivity
(b) conductivity
(c) potential difference
(d) resistance

(a)
Explanation:
J =σE ⇒ Jρ=E
J is current density, E is electric field
so B = ρ = resistivity.

Q.6. Drift velocity of electrons is due to
(a) motion of conduction electrons due to random collisions.
(b) motion of conduction electrons due to electric field E
(c) repulsion to the conduction electrons due to inner electrons of ions.
(d) collision of conduction electrons with each other.

(b)
Explanation:
Motion of conduction electrons due to random collisions has no preffered direction and average to zero. Drift velocity is caused due to motion of conduction electrons due to applied electric field E.

Q.7. The speed at which the current travels, in conductor, is nearly equal to
(a) 3 × 104 m/s
(b) 3 × 105 m/s
(c) 4 × 106 m/s
(d) 3 × 108 m/s

(d)

Q.8. In the absence of an electric field, the mean velocity of free electrons in a conductor at absolute temperature (T) is
(a) zero
(b) independent of T
(c) proportional to T
(d) proportional to T2

(a)

Q.9. When a potential difference V is applied across a conductor at a temperature T, the drift velocity of electrons is proportional to
(a) V
(b) V
(c) T
(d) T

(b)

Q.10. For which of the following dependence of drift velocity vd on electric field E, is Ohm’s law obeyed?
(a) vd α E2
(b) vd = E1/2
(c) vd = constant
(d) vd = E

(d)

Q.11. The current density (number of free electrons per m3) in metallic conductor is of the order of
(a) 1022
(b) 1024
(c) 1026
(d) 1028

(d)

Q.12. A current passes through a resistor. If K1 and K2 represent the average kinetic energy of the conduction electrons and the metal ions respectively then
(a) K1 < K2
(b) K1 = K2
(c) K1 > K2
(d) any of these three may occur

(c)

Q.13. A metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases, the drift velocity of the electron in it
(a) increases, thermal velocity of the electron increases
(b) decreases, thermal velocity of the electron increases
(c) increases, thermal velocity of the electron decreases
(d) decreases, thermal velocity of the electron decreases

(b)
Explanation:
When the temperature increases, resistance increases. As the e.m.f. applied is the same, the current density decreases the drift velocity decreases. But the rms velocity of the electron due to thermal motion is proportional to √T . The Thermal velocity increases.

Q.14. The electric field intensity E, current density J and specific resistance k are related to each other through the relation
(a) E = J/k
(b) E = J k
(c) E = k/J
(d) k = J E

(b)

Q.15. The relaxation time in conductors
(a) increases with the increases of temperature
(b) decreases with the increases of temperature
(c) it does not depends on temperature
(d) all of sudden changes at 400 K

(b)
Explanation:
Because as temperature increases, the resistivity increases and hence the relaxation time decreases for conductors

Q.16. We are able to obtain fairly large currents in a conductor because
(a) the electron drift speed is usually very large
(b) the number density of free electrons is very high and this can compensate for the low values of the electron drift speed and the very small magnitude of the electron charge
(c) the number density of free electrons as well as the electron drift speeds are very large and these compensate for the very small magnitude of the electron charge
(d) the very small magnitude of the electron charge has to be divided by the still smaller product of the number density and drift speed to get the electric current

(b)

Q.17. In conductor when electrons move between two collisions, their paths are … A… when external fields are absent and … B…when external filed is present. Here, A and B refer to
(a) straight lines, straight lines
(b) straight lines, curved lines
(c) curved lines, straight lines
(d) curved lines, curved lines

(b)
Explanation:
In conductor when electrons move between two collisions, their paths are straight lines when external fields are absent and paths are curved in general when external field is present.

Q.18. The effective resistance between C & D in given circuit is

(a) R
(b) 3R
(c) 2R/3
(d) R/3

(c) 2R/3

Q.19. Two or more resistors are said to be in …A… if one end of all resistors is joined together and similarly the other ends joined together, Here, A refers to
(a) series
(b) parallel
(c) either (a) or (b)
(d) None of these

(b)

Q.20. The example of non-ohmic resistance is
(a) diode
(b) copper wire
(c) filament lamp
(d) carbon resistor

(a)

Q.21. Constantan wire is used for making standard resistance, because it has
(a) high melting point
(b) low specific resistance
(c) high specific resistance
(d) negligible temperature coefficient of resistance

(d)

Q.22. At temperature 0K, the germanium behaves as a / an
(a) conductor
(b) insulator
(c) super-conductor
(d) ferromagnetic

(b)

Q.23. Which of the following is used for the formation of thermistor?
(a) Copper oxide
(b) Nickel oxide
(c) Iron oxide
(d) All of the above

(d)

Q.24. What is the suitable material for electric fuse?
(a) Cu
(b) Constantan
(d) Nichrome

(c)

Q.25. A strip of copper and another of germanium are cooled from room temperature to 80 K. The resistance of
(a) each of these increases
(b) each of these decreases
(c) copper strip increases and that of germanium decreases
(d) copper strip decreases and that of germanium increases

(d)

Q.26. The electric resistance of a certain wire of iron is R. If its length and radius are both doubled, then
(a) the resistance and the specific resistance, will both remain unchanged
(b) the resistance will be doubled and the specific resistance will be halved
(c) the resistance will be halved and the specific resistance will remain unchanged
(d) the resistance will be halved and the specific resistance will be doubled

(c)

Q.27. Nichrome or Manganin is widely used in wire bound standard resistors because of their
(a) temperature independent resistivity
(b) very weak temperature dependent resistivity.
(c) strong dependence of resistivity with temperature.
(d) mechanical strength.

(b) These materials exhibit a very weak dependence of resistivity on temperature. Their resistance values would be changed very little with temperature as shown in figure. Hence these materials are widely used as heating element.

Q.28. With increase in temperature the conductivity of
(a) metals increases and of semiconductor decreases.
(b) semiconductors increases and metals decreases.
(c) in both metals and semiconductors increases.
(d) in both metal and semiconductor decreases.

(b) Semiconductors having negative temperature coefficient of resistivity whereas metals are having positive temperature coefficient of resistivity with increase in temperature the resistivity of metal increases where a resistivity of semiconductor decreases.

Q.29. The resistance of a metal increases with increasing temperature because
(a) the collisions of the conducting electrons with the electrons increase
(b) the collisions of the conducting electrons with the lattice consisting of the ions of the metal increase
(c) the number of conduction electrons decreases
(d) the number of conduction electrons increases

(a) decreases.

Q.30. To minimise the power loss in the transmission cables connecting the power stations to homes and factories, the transmission cables carry current
(a) at a very low voltage.
(b) at a very high voltage
(c) at 220 volt
(d) neither at a very high voltage nor at a very low voltage.

(b) The power dissipated in the transmission cables is inversely proportional to the square of voltage at which current is transmitted through the cables. Therefore to minimize the power loss the transmission cables carry current at a very high voltage.

Q.31. Appliances based on heating effect of current work on
(a) only a.c.
(b) only d.c.
(c) both a.c. and d.c.
(d) None of these

(c)

Q.32. In the series combination of two or more than two resistances
(a) the current through each resistance is same
(b) the voltage through each resistance is same
(c) neither current nor voltage through each resistance is same
(d) both current and voltage through each resistance are same.

(a) In series combination, current across its circuit components is always constant and in parallel combination the voltage across the circuit components in constant.

Q.33. Emf of a cell is
(a) the maximum potential difference between the terminals of a cell when no current is drawn from the cell.
(b) the force required to push the electrons in the circuit.
(c) the potential difference between the positive and negative terminal of a cell in a closed circuit.
(d) less than terminal potential difference of the cell.

(a)

Q.34. To draw a maximum current from a combination of cells, how should the cells be grouped?
(a) Parallel
(b) Series
(c) Mixed grouping
(d) Depends upon the relative values of internal and external resistances.

(d)

Q.35. The resistance of the coil of an ammeter is R. The shunt required to increase its range n-fold should have a resistance (a) R/n (b) R/(n-1) (c) R/(n+1) (d) nR

(b)

Q.36. A cell of internal resistance r is connected across an external resistance nr. Then the ratio of the terminal voltage to the emf of the cell is (a) 1/n (b) 1/(n+1) (c) n/(n+1) (d) (n-1)/n

(c)

Q.37. When potential difference is applied across an electrolyte, then Ohm’s law is obeyed at
(a) zero potential (b) very low potential
(c) negative potential (d) high potential

(d)

Q.38. Under what condition will the strength of current in a wire of resistance R be the same for connection is series and in parallel of n identical cells each of the internal resistance r? When
(a) R = n r (b) R = r/n
(c) R = r (d) R → ∞, r → 0

(d)

Q.39. A cell of internal resistance r is connected to an external resistance R. The current will be maximum in R, if
(a) R = r (b) R < r (c) R > r (d) R = r/2

(a)

Q.40. An energy source will supply a constant current into the load if its internal resistance is
(a) very large as compared to the load resistance
(b) equal to the resistance of the load
(c) non-zero but less than the resistance of the load
(d) zero

(d)

Q.41. Kirchhoff’s first law, i.e., ∑ i = 0 at a junction, deals with the conservation of
(a) charge (b) energy
(c) momentum (d) angular momentum

(a)

Q.42. The Kirchhoff’s second law (∑iR = ∑E), where the symbols have their usual meanings, is based on
(a) conservation of momentum
(b) conservation of charge
(c) conservation of potential
(d) conservation of energy

(d) Kirchhoff’s first law is based on conservation of charge and Kirchhoff’s second law is based on conservation of energy.

Q.43. Why is the Wheatstone bridge better than the other methods of measuring resistances?
(a) It does not involve Ohm’s law
(b) It is based on Kirchhoff’s law
(c) It has four resistor arms
(d) It is a null method

(d)

Q.44. If in the experiment of Wheatstone’s bridge, the positions of cells and galvanometer are interchanged, then balance point will
(a) change
(b) remain unchanged
(c) depend on the internal resistance of cell and resistance of galvanometer
(d) None of these

(b)

Q.45. In a Wheatstone bridge in the battery and galvanometer are interchanged then the deflection in galvanometer will
(a) change in previous direction
(b) not change
(c) change in opposite direction
(d) none of these.

(b) The deflection in galvanometer will not be changed due to interchange of battery and the galvanometer.

Q.46. In meter bridge or Wheatstone bridge for measurement of resistance, the known and the unknown resistance are interchanged. The error so removed is
(a) end correction
(b) index error
(c) due to temperature effect
(d) random error

(a) In meter bridge experiment, it is assumed that the resistance of the L shaped plate is negligible, but actually it is not so. The error created due to this is called end error. To remove this the resistance box and the unknown resistance must be interchanged and then the mean reading must be taken.

Q.47. Potentiometer is based on
(a) deflection method
(b) zero deflection method
(c) both (a) and (b)
(d) None of these

(b) Potentiometer is based on zero deflection method.

Q.48. In potentiometer a balance point is obtained, when
(a) the e.m.f. of the battery becomes equal to the e.m.f of the experimental cell
(b) the p.d. of the wire between the +ve end of battery to jockey becomes equal to the e.m.f. of the experimental cell
(c) the p.d. of the wire between +ve point of cell and jockey becomes equal to the e.m.f. of the battery
(d) the p.d. across the potentiometer wire becomes equal to the e.m.f. of the battery

(b)

Q.49. Potentiometer measures potential more accurately because
(a) it measures potential in open circuit
(b) it uses sensitive galvanometer for null deflection
(c) it uses high resistance potentiometer wire
(d) it measures potential in closed circuit

(a)

Q.50. For measuring voltage of any circuit, potentiometer is preferred to voltmeter because
(a) the potentiometer is cheap and easy to handle.
(b) calibration in the voltmeter is sometimes wrong .
(c) the potentiometer almost draws no current during measurement.
(d) range of the voltmeter is not as wide as that of the potentiometer.

(c)

Q.51. In the experiment of potentiometer, at balance point, there is no current in the
(a) main circuit
(b) galvanometer circuit
(c) potentiometer circuit
(d) both main and galvanometer circuits

(b)

Q.52. Sensitivity of potentiometer can be increased by
(a) increasing the e.m.f of the cell
(b) increasing the length of the potentiometer
(c) decreasing the length of the potentiometer wire
(d) None of these

(b)

## Quiz on Current Electricity

General Instructions:

(1) Total number of question is 5.

(2) Each question has 4 choices, out of which ONLY ONE CHOICE is correct.

1.
A wire has resistance 16 Ω . It is bent in the form of an equilateral triangle. The effective resistance between the two points on any median of the triangle is

2.
Choose the correct alternative:

3.
The current in a metallic conductor is plotted against voltage at two different temperatures T1 and T2. Choose the correct answer. 4.
Two electric lamps A and B having power 200 watt and 100 watt respectively are rated on the same voltage. The ratio of resistance of lamp A to that of B is :

5.
A battery of emf E and internal resistance r is connected across a resistance R. Resistance R can be adjusted to any value greater than or equal to zero. A graph is plotted between the current (i) passing through the resistance and potential difference (V) across it. Select the correct alternative(s). One App For All Your Needs.

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