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Current Electricity Class 12 MCQs Questions with Answers
Question 1.
Kirchhoff s second law is based on the law of conservation of
(a) charge
(b) mass
(c) energy
(d) momentum
Answer
Answer: (c) energy
Question 2.
When there is an electric current through a conducting wire along its length, then an electric field must exist:
(a) outside the wire but normal to it.
(b) inside the wire but parallel to it.
(c) inside the wire but normal to it.
(d) outside the wire but around it.
Answer
Answer: (b) inside the wire but parallel to it.
Question 3.
The terminal potential difference of a cell when short circuited is
(a) zero
(b) E
(c) \(\frac {E}{2}\)
(d) \(\frac {E}{3}\)
Answer
Answer: (a) zero
Question 4.
A cell of e.m.f. ‘E’ and internal resistance r is connected in series with an external resistance nr. Then the ratio of the terminal potential difference to e.m.f. is
(a) \(\frac {1}{n}\)
(b) \(\frac {1}{n+1}\)
(c) \(\frac {n}{n+1}\)
(d) \(\frac {n+1}{n}\)
Answer
Answer: (c) \(\frac {n}{n+1}\)
Question 5.
For which of the following dependence of drift velocity electric field E is Ohm’s law obeyed.
(a) vd < √E
(b) vd ∝ E
(c) vd ∝ E²
(d) vd = constant
Answer
Answer: (b) vd ∝ E
Question 6.
In 10 minutes, 3000 Coulombs of free electrons enter one end of a conductor and 3000 Coulomb of then leave the conductor at its other end. The current in the conductor is:
(a) 5 A
(b) 10 A
(c) 0 A
(d) 30 A
Answer
Answer: (a) 5 A
Question 7.
A current I flows in a wire of circular cross-section with the free electrons travelling with a drift velocity v. The drift velocity of electrons when a current 21 flows in another wire of twice radius and of the same material is:
(a) \(\frac {v}{2}\)
(b) v
(c) 2v
(d) √2 v
Answer
Answer: (a) \(\frac {v}{2}\)
Question 8.
Three equal registers connected in series across a source of e.m.f. together dissipate 10 watts of power. What would be the power dissipated if the same resistors are connected in parallel across the same source of e.m.f.?
(a) 9 watts
(b) 90 watts
(c) 10 watts
(d) 100 watts
Answer
Answer: (b) 90 watts
Question 9.
The temperature coefficient of resistance of a wire is 0.00125° C-1. At 27°C, its resistance is 1Ω. The temperature of the wire at which its resistance becomes 2Ω is:
(a) 1400 K
(b) 854°C
(c) 1127 K
(d) 1154 K.
Answer
Answer: (b) 854°C
Question 10.
The heating element of an electric heater should be made of a material that should have:
(a) low specific resistance and low melting point.
(b) high specific resistance and high melting point.
(c) high specific resistance and low melting point.
(d) low specific resistance and high melting point.
Answer
Answer: (b) high specific resistance and high melting point.
Question 11.
The effective wattage of 60 W and 40 W lamps connected in: (A) series is equal to:
(a) 24 W
(b) 20 W
(c) 100 W
(d) 80 W.
Answer
Answer: (a) 24 W
(B) parallel is equal to:
(a) 24 W
(b) 20 W
(c) 100 W
(d) 80 W
Answer
Answer: (c) 100 W
Question 12.
In an experiment to measure the internal resistance of a cell by a potentiometer, it is found that the balance point is at a length of 2 m, when the cell is shunted by a 5Ω resistance and is at 3 m when the cell is shunted by a 10Ω resistance. The internal resistance of the cell is:
(a) 10 Ω
(b) 15 Ω
(c) 1 Ω
(d) 1.5 Ω
Answer
Answer: (a) 10 Ω
Fill in the Blanks
Question 1.
For ‘n’ identical resistances, the ratio of the total resistances of series combination to the total resistance of parallel combination is ……………….
Answer
Answer: \(\frac {R_s}{R_p}\) = n²
Question 2.
The drift velocity of electron is of the order of ………………. while the thermal average thermal velocity of the electron at room temperature is ……………….
Answer
Answer: 10-5 ms-1, 105 to 106 ms-1.
Question 3.
The temperature coefficient of resistance lies between ………………. to ………………. °C-1
Answer
Answer: 10-2, 10-4
Question 4.
Manganin has a resistance which is ………………. taken as compared to pure copper and its temperature coefficient is ………………. °C-1.
Answer
Answer: 30 to 40, 10-5
Question 5.
The resistivity of a conductor depends upon the nature of the material of the conductor but is independent of the ……………….
Answer
Answer: Physical dimensions i.e., length and area of cross-section of the conductor.
Question 6.
The direction of current inside the cell is from ………………. electrode but outside the cell, it is from ………………. electrode.
Answer
Answer: negative to positive electrode, positive to negative electrtode.
Question 7.
The terminal potential difference of a cell is zero when the potential drop across its internal resistance is ………………. while for the cell to be in open circuit the terminal P.D. is ……………….
Answer
Answer: equal to the e.m.f. of the cell, equal to tfie e.m.f. fo the cell.
Question 8.
In order to get a large amount of current from the cells connected in series, the external resistance should be ……………….
Answer
Answer: Very large as compared to the net internal resistance of the cells.
Question 9.
In order to get the maximum current in the circuit, the mixed grouping of cells must be done in such a way that the external resistance is ……………….
Answer
Answer: equal to the net (effective) internal resistance of all the cells.
Question 10.
Nichrome is an alloy of ………………., ………………. and ……………….
Answer
Answer: Ni, Cu, Cr.
Question 11.
Commercial unit of electrical energy is ………………. and is ………………. times the J.
Answer
Answer: KWh or B.O.T. unit or simply unit, 3.6 × 106.
Question 12.
For the wheatstone bridge to be balanced, the necessary conditions for the four resistances is ……………….
Answer
Answer: \(\frac {P}{Q}\) = \(\frac {R}{X}\)
Question 13.
For a potentiometer, the ratio of the e.m.f.s of two cells is ……………….
Answer
Answer: equal to the ratio of the balancing lengths for the two cells i.e., mathematically, \(\frac {E_1}{E_2}\) = \(\frac {l_1}{l_2}\).
Question 14.
For insulators, the resistance ………………. with the increase in temperature.
Answer
Answer: increases.
Question 15.
The relation ………………. is used when supplied electric power is lost or dissipated as heat.
Answer
Answer: P = I²R.
Question 16.
The equivalent resistance of a network ………………. due to parallel grouping of resistances and becomes ……………….
Answer
Answer: decrease, lesser than the least resistance in the network.
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