Current Electricity

Current Electricity Class 12 Physics MCQs

1. An electric heater is connected to the voltage supply. After few seconds, current gets its steady value then its initial current will be
(a) equal to its steady current
(b) slightly higher than its steady current
(c) slightly less than its steady current
(d) zero

2. 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 re-sistance is same.
(d) both current and voltage through each resis¬tance are same.

3. Combine three resistors 5 Q, 4.5 Q and 3 Q in such a way that the total resistance of this combination is maximum
(a) 12.5 Q
(b) 13.5 Q
(c) 14.5 Q
(d) 16.5 Q

4. A cell having an emf E and internal resistance r is connected across a variable external resistance R. As the resistance R is increased, the plot of potential difference V across R is given by

5. In parallel combination of n cells, we obtain
(a) more voltage
(b) more current
(c) less voltage
(d) less current

6. If n cells each of emf e and internal resistance r are connected in parallel, then the total emf and internal resistance will be

7. In a Wheatstone bridge if 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.

8. When a metal conductor connected to left gap of a meter bridge is heated, the balancing point
(a) shifts towards right
(b) shifts towards left
(c) remains unchanged
(d) remains at zero

9. In a potentiometer of 10 wires, the balance point is obtained on the 7^th wire. To shift the balance point to 9th wire, we should
(a) decrease resistance in the main circuit.
(b) increase resistance in the main circuit.
(c) decrease resistance in series with the cell whose emf is to be measured.
(d) increase resistance in series with the cell whose emf is to be determined.

10. AB is a wire of potentiometer with the increase in the value of resistance R, the shift in the balance point J will be

(a) towards B
(b) towards A
(c) remains constant
(d) first towards B then back towards A.

11. A charge is moving across a junction, then
(a) momentum will be conserved.
(b) momentum will not be conserved.
(c) at some places momenturii will be conserved and at some other places momentum will not be conserved.
(d) none of these.

12. Which of the following I-V graph represents ohmic conductors?

13. The I-V characteristics shown in figure represents

(a) ohmic conductors
(b) non-ohmic conductors
(c) insulators
(d) superconductors

14. Which of the following is correct for V-I graph of a good conductor?

15. The resistivity of alloy manganin is
(a) Nearly independent of temperature
(b) Increases rapidly with increase in temperature
(c) Decreases with increase in temperature
(d) Increases rapidly with decrease in temperature

Question 16.
The speed at which tjie current travels in a conductor is nearly:
(a) 3 × 10⁴ ms^-1
(b) 3 × 10⁶ ms^-1
(c) 3 × 10⁸ ms^-1
(d) 3 × 10¹⁰ ms^-1

Question 17.
The resistance of a human body is about:
(a) 12 Ω
(b) 120 Ω
(c) 12 KΩ
(d) 120 MΩ

Question 18.
The number of electrons that constitute 1 A of current is:
(a) 6.25 × 10¹⁶
(b) 6.25 × 10¹⁷
(c) 6.25 × 10¹⁸
(d) 6.25 × 10¹⁹

Question 19.
How many different resistances are possible with two equal resistors?
(a) 2
(b) 3
(c) 4
(d) 5

Question 20.
Given three equal resistors, how many different combinations (taken all of them together) can be made?
(a) 3
(b) 4
(c) 5
(d) 6

Question 21.
Specific resistance of ali metals is mostly affected by:
(a) temperature
(b) pressure
(c) magnetic field
(d) volume

Question 22.
The example of a non-ohmic resistance is:
(a) copper wire
(b) fi lament lamp
(c) carbon resistor
(d) diode

Question 23.
If a certain piece of copper is to be shaped into a conductor of minimum resistance, its length (L) and cross-sectional area (a) shall respectively be :
(a) L, 2A
(b) \(\frac{L}{2}\), 2A
(c) 2L, 2A
(d) 2l, \(\frac{A}{2}\)

Question 24.
The specific resistance of a rod of copper as compared to that of thin wire of copper is :
(a) less
(b) more
(c) same
(d) depends upon the length and area of cross-section of the wire

Question 25.
A wire of resistance 3 Ω is cut into three pieces, which are then joined to form a triangle. The equivalent resistance between any corners of the triangle is :
(a) \(\frac{2}{3}\) Ω
(b) \(\frac{3}{2}\) Ω
(c) \(\frac{1}{2}\) Ω
(d) \(\frac{1}{3}\) Ω

Question 26.
The length of a conductor is halved. Its resistance will be :
(a) halved
(b) doubled
(c) unchanged
(d) quadrupled

Question 27.
In the above question, the conductance:
(a) halved
(b) doubled
(c) unchanged
(d) quadrupled

Question 28.
Siemen is the unit of:
(a) resistance
(b) conductance
(c) specific conductance
(d) None of these

Question 29.
How much electric energy is consumed by a 100 W lamp used for 6 hours everyday for 30 days?
(a) 18 kJ
(b) 18 kWh
(c) 1.8 J
(d) None of these

Question 30.
Suppose H₁ is the heat generated per second in the filament of a 100 W, 250 V lamp and H₂ is the heat generated in the filament of a 200 W, 250 V lamp. Then H₁/H₂ is equal to:
(a) 1
(b) 2
(c) \(\frac{1}{2}\)
(d) \(\frac{1}{4}\)

Question 31.
Two wires of copper are of the same length but’have different diameters. When they are connected in series across a battery, the heat generated is H₁ When connected in parallel across the same battery, the heat generated during the same time is H₂ Then :
(a) H₁ = H₂
(b) H₁ < H₂
(c) H₁ > H₂
(d) H₁ > H₂

Question 32.
In questions 135, w hen the wires are connected in series, the heat produced in the thinner wire is H₁ and that in the thicker wire is H₂. Then :
(a) H₁ = H₂
(b)H₁ < H₂
(c) H₁ > H₂
(d) H₁ > H₂

Question 33.
Kirchhoffs first and second laws for electrical circuits are consequences of:
(a) conservation of energy
(b) conservation of electrical charge and energy respectively
(c) conservation of electric charge
(d) neither conservation of energy nor electric charge

Question 34.
A 5 A fuse wire can with stand a maximum power of 1 W in circuit. The resistance of the fuse wire is:
(a) 0.2 Ω
(b) 5 Ω
(c) 0.4 Ω
(d) 0.04 Ω

Question 35.
The length and radius of an electric resistance of a certain wire are doubled simultaneously, then the:
(a) resistance will be doubled and specific resistance will be halved
(b) resistance will be halved and specific resistance will remain uncharged
(c) resistance will be halved and the specific resistance will be doubled
(d) resistance and specific resistance will both remain uncharged

Question 36.
A galvanometer acting as a volt meter will have with its coil.
(a) a high resistance in parallel
(b) a high resistance in series
(c) a low resistance in parallel
(d) a low resistance in series

Question 37.
When three identical bulbs of 60 W, 200 V rating are connected in series to a 200 V supply, the power drawn by them will be:
(a) 20 W
(b) 60 W
(c) 180 W
(d) 10 W

Question 38.
n resistances, each of R Ω, are connected in parallel gives an equivalent resistance of R Ω. If these resistances were , connected in series, the combination would have a resistance in Ω is equal to
(a) n²R
(b) R/n²
(c) R/n
(d) nR

Question 39.
Why is the Wheatstone bridge more accurate than other methods of measuring resistances: ‘
(a) It is a null method
(b) It is based on Kirchhoffs laws
(c) It has four resistances
(d) It does not involve ohm’s law

Question 40.
A potential difference of 10 V is applied across a conductance of 2 S. The current in the conductor will be :
(a) 20 A
(b) 5 A
(c) 0.2 A
(d) None of these

Question 41.
Ohm’s law is valid when the temperature of conductor is :
(a) very low
(b) very high
(c) varying
(d) constant

Question 42.
The emf of a car battery is about:
(a) 2.5 V
(b) 4.5 V
(c) 8.6 V
(d) 12 V

Question 43.
Emf is measured in :
(a) joule
(b) joule/coulomb
(c) joule-coulombs
(d) joule/coulomb/metre

Question 44.
1 kilowatt hour is commonly known as :
(a) unit
(b) 1 faraday
(c) 1 curie
(d) None of these

Question 45.
How many joules are equal to I kWh ?
(a) 3.6 × 10⁴
(b) 3.6 × 10⁵
(c) 3.6 × 10⁶
(d) None of these

Question 46.
The temperature coefficient of resistance is expressed in :
(a) °C
(b) °C^-1
(c) m°C^-1
(d) None of these

Question 47.
Copper wire is used as connecting wire because :
(a) copper has high electrical resistivity
(b) copper has low electrical resistivity
(c) copper has low electrical conductivity
(d) copper has high value of elasticity

Question 48.
The heat sensitive device whose resistivity changes very rapidly with change of temperature is called a :
(a) resistor
(b) super-conductor
(c) thermocouple
(d) thermistor

Question 49.
The phenomenon of super-conductivity was discovered by :
(a) Ohm
(b) Onnes
(c) Edison
(d) None of these

Question 50.
The specific resistance of a conductor increases with :
(a) increase in temperature
(b) increase in cross-sectional area
(c) decrease in length
(d) decrease in cross-sectional area

Question 51.
In an experiment with potentiometer, null point with a cell is found at 240 cm. When the cell is shunted with a resistance 2 Ω, the null point becomes 120 cm internal resistance of cell is :
(a) 4 Ω
(b) 2 Ω
(c) 1 Ω
(d) \(\frac{1}{2}\) Ω

Question 52.
Two conductors of equal length and radii the ratio of 2 : 3 are; connected in parallel the source of electricity. The ratio of the velocity of electrons in the conductor be :
(a) 2 : 3
(b) 4 : 9
(c) 1 : 1
(d) 3 : 2

Question 53.
The charge flowing in a conductor varies with time as :
q = αt \(\frac{1}{2}\) βt² + \(\frac{1}{6}\) γt³
Where α, β, γ are positive constants. Then the initial current (l) is given by the condition :
(a) l = α
(b) l = α²
(c) l = α^-1
(d) None of these

Question 54.
In questions 38, the maximum value of current (l_max) is given by the condition :
(a) l_max = α – \(\frac{β^2}{2γ}\)
(b) l_max = α – \(\frac{β^2}{2α}\)
(c) l_max = α – \(\frac{γ^2}{2β}\)
(d) None of these

Question 55.
In questions 38, the line (t) after which the value of current reaches a maximum values given by :
(a) t = \(\frac{α}{β}\)
(b) t = \(\frac{β}{α}\)
(c) t = \(\frac{β}{γ}\)
(d) t = \(\frac{γ}{β}\)

Question 56.
In following figure shows currents in a part of electrical circuit, then the value of/(in ampere) is given by :

(a) 0.3 A
(b) 0.5 A
(c) 1.3 A
(d) None of these

Question 57.
The smallest resistance that can be obtained by the combination of n resistors each resistance r is :
(a) \(\frac{r}{n}\)
(b) nr
(c) \(\frac{n}{r}\)
(d) n²r

Question 58.
Which of the following has a negative temperature coefficient of resistance ?
(a) Tungsten
(b) Carbon
(c) Nichrome
(d) Platinum

Question 59.
An electric heating element consumes 500 W, when connected to a 100 V line. If the line voltage becomes 150 V, the power consumed Will be:
(a) 500 W
(b) 750 W
(c) 1000 W
(d) 1125 W

Question 60.
A uniform w ire connected across a supply produces heat H per second. If wire is cut into three equal parts and all the parts are connected in parallel across the same supply, the heat produced per second will be :
(a) \(\frac{H}{9}\)
(b) 9 H
(c) 3 H
(d) \(\frac{H}{3}\)

Question 61.
In India electricity is supplied fordomestic use at 220 V. It is supplied at 110 V in U.S.A. If the resistance of a 60 W bulb use in India is R. the resistance of a 60 W bulb for use in USA will be:
(a) 2 R
(b) R
(c) R/2
(d) R/4

Question 62.
In the following figure represents a balanced Wheatstone bridge circuit. What is the value of X ?

(a) 15 Ω
(b) 20 Ω
(c) 25 Ω
(d) 30 Ω

Question 63.
Two bulbs 25 W, 220 V and 100 W, 220 V are given. Which has higher resistance?
(a) 25 W
(b) 100 W
(c) both bulbs have equal resistance
(d) resistance of bulbs can not be compared

Question 64.
Potentiometer measures the potential difference more accurately than a voltmeter because:
(a) It has a wire of high resistance
(b) It has a wire of low resistance
(c) It does not draw current from external circuit
(d) It draws heavy current from external circuit

Question 65.
In a Wheatstone bridge, the resistance each arm is 10 Ω. If the resistance galvanometers is also 10 Ω, then effective resistance of the bridge will be :
(a) 40 Ω
(b) 20 Ω
(c) 10 Ω
(d) 5 Ω

Question 66.
The resistance of an aluminium wire is/i. It is stretched to /i times its original length. Its new resistance will be :
(a) nr
(b) n²r
(c) \(\frac{n^2}{r}\)
(d) \(\frac{r}{n^2}\)

Question 67.
A wire P is half the diameter and half the length of a wire Q of similar material. The ratio of resistances of P to that 0 is:
(a) 4 : 1
(b) 8 : 1
(c) 2 : 1
(d) 1 : 2

Question 68.
What is the resistance across A and B in the network in Fig.?
(a) R
(b) 2 R
(c) \(\frac{R}{2}\)
(d) 6 R

Question 69.
When the wires are connected in parallel, the heat produced in the thinner wire is H₁ and that in the thicker wire is H₂ Then:
(a) H₁ = H₂
(b) H₁ < H₂
(c) H₁ > H₂
(d) H₁ ≥ H₂

Question 70.
Two equal resistors are connected in series across a battery and consume a power of P. If these are connected in parallel, then the’ power consumed will be:
(a) 2P
(b) 4P
(c) \(\frac{p}{4}\)
(d) P

Question 71.
Thermo electricity was discovered by:
(a) Joule
(b) Peitier
(c) Thomson
(d) Seebeck

Question 72.
Thermo emf is the order of:
(a) 10 V
(b) 10^-3 V
(c) 10^-6 V
(d) 10^-12 V