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NCERT Solutions for class 12 Physics | Chapter 3 - Current Electricity

(1) In a potentiometer of 10 wires, the balance point is obtained on the 7th 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.
Answer: increase resistance in series with the cell whose emf is to be determined.
(2) In parallel combination of n cells, we obtain
[A] more voltage
[B] more current
[C] less voltage
[D] less current
Answer: more current

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(3) 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.
Answer: the current through each resistance is same.
(4) 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.
Answer: none of these.
(5) 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.
Answer: not change
(6) 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
Answer: shifts towards right
(7) 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
Answer: slightly higher than its steady current
(8) The I-V characteristics shown in figure represents

[A] ohmic conductors
[B] non-ohmic conductors
[C] insulators
[D] superconductors
Answer: non-ohmic conductors
(9) 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.
Answer: towards B
(10) 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
Answer: 12.5 Q
(11) 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
Answer: Nearly independent of temperature
(12) If n cells each of emf e and internal resistance r are connected in parallel, then the total emf and internal resistance will be
[A]
[B] ε,nr
[C]
[D] nε, nr
Answer:
(13) 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
[A]
[B]
[C]
[D]
Answer:
(14) Thermo electricity was discovered by:
[A] Joule
[B] Peitier
[C] Thomson
[D] Seebeck
Answer: Seebeck
(15) 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
Answer: H1 < H2
(16) 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
Answer: 2 : 1
(17) 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
Answer: 10 Ω
(18) 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
Answer: 25 W
(19) 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
Answer: R/4
(20) Which of the following has a negative temperature coefficient of resistance ?
[A] Tungsten
[B] Carbon
[C] Nichrome
[D] Platinum
Answer: Carbon

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