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Current Electricity MCQs — Physics (page 4)

270 multiple-choice questions on Current Electricity from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

76. A cell transfers 18 J of energy to 3 C of charge driven round a complete circuit. Its e.m.f. is:

  1. 54 V
  2. 12 V
  3. 6 V
  4. 3 V

Answer: C) 6 V

Explanation: mathcalE = WQ = 6 V. SLO P-09-E-15 · Application

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77. A current of 0.2 A flows through a 100 Ω resistor. The power dissipated is:

  1. 4 W
  2. 8 W
  3. 20 W
  4. 2 W

Answer: A) 4 W

Explanation: P = I^2R = (0.2)^2(100) = 4 W. SLO P-09-E-12 · Application

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78. A loop has a 12 V cell and resistors of 2 Ω and 4 Ω in series. The current is:

  1. 6 A
  2. 2 A
  3. 3 A
  4. 0.5 A

Answer: B) 2 A

Explanation: 12 = I(2 + 4). SLO P-09-E-19 · Understanding

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79. A standard cell of e.m.f. 2 V balances at 50 cm on a potentiometer wire. Another cell balances at 35 cm. Its e.m.f. is:

  1. 0.7 V
  2. 2.8 V
  3. 1.4 V
  4. 2.86 V

Answer: C) 1.4 V

Explanation: mathcalE2mathcalE1 = l2l1 Rightarrow mathcalE2 = 2 3550 = 1.4 V. SLO P-09-E-23 · Application

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80. A cell has an e.m.f. of 1.5 V. When it drives a current, the p.d. across its terminals is usually:

  1. 3 V
  2. exactly 0 V
  3. more than 1.5 V
  4. slightly less than 1.5 V

Answer: D) slightly less than 1.5 V

Explanation: Some energy is lost inside the cell. SLO P-09-E-16 · Understanding

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81. Going through a cell from the negative to the positive terminal, the potential:

  1. falls by the e.m.f.
  2. stays the same
  3. rises by the e.m.f.
  4. becomes zero

Answer: C) rises by the e.m.f.

Explanation: Sign convention. SLO P-09-E-19 · Understanding

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82. Resistance in the carbon fibre network is measured by:

  1. passing a small current and measuring the p.d.
  2. listening to the bridge
  3. measuring its temperature only
  4. weighing the bridge

Answer: A) passing a small current and measuring the p.d.

Explanation: R = V/I. SLO P-09-E-27 · Understanding

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83. The e.m.f. of a source is:

  1. the force on electrons
  2. the resistance of the source
  3. the energy transferred per unit charge in driving charge round a complete circuit
  4. the current from the source

Answer: C) the energy transferred per unit charge in driving charge round a complete circuit

Explanation: Not a force despite its name. SLO P-09-E-15 · Application

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84. Short-circuiting a battery is dangerous because:

  1. a very large current flows, heating the battery
  2. the e.m.f. becomes infinite
  3. no current flows
  4. it reverses the battery

Answer: A) a very large current flows, heating the battery

Explanation: Current limited only by r. SLO P-09-E-17 · Understanding

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85. In the same circuit, the current in the 3 Ω resistor is:

  1. 2 A
  2. 23 A
  3. 43 A
  4. 1 A

Answer: C) 43 A

Explanation: 4/3 A; check: 23 + 43 = 2 A (first law). SLO P-09-E-22 · Application

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86. A potentiometer wire 100 cm long has a potential gradient of 0.015 V/cm. A thermocouple balances at 40 cm. Its e.m.f. is:

  1. 0.6 V
  2. 2.67 V
  3. 0.06 V
  4. 6 V

Answer: A) 0.6 V

Explanation: mathcalE = 0.015 40. SLO P-09-E-23 · Application

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87. Kirchhoff's second law is a consequence of the conservation of:

  1. momentum
  2. energy
  3. mass
  4. charge

Answer: B) energy

Explanation: Energy gained by a charge round a loop = energy lost. SLO P-09-E-19 · Understanding

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88. The terminal p.d. V of a source with e.m.f. mathcalE and internal resistance r delivering current I is:

  1. V = mathcalE + Ir
  2. V = mathcalE - Ir
  3. V = mathcalEIr
  4. V = Ir

Answer: B) V = mathcalE - Ir

Explanation: Lost volts inside the source. SLO P-09-E-17 · Understanding

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89. Heating elements use nichrome because it has:

  1. low melting point
  2. high resistivity and a high melting point
  3. very low resistivity
  4. zero resistance

Answer: B) high resistivity and a high melting point

Explanation: Produces heat without melting. SLO P-09-E-13 · Application

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90. A wire's cross-sectional area doubles along its length while current stays the same. In the thicker part the drift speed:

  1. halves
  2. stays the same
  3. doubles
  4. becomes zero

Answer: A) halves

Explanation: Same I and n. SLO P-09-E-10 · Application

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91. A 9 V battery (no internal resistance) is connected to three resistors in series. The p.d.s across two of them are 2.5 V and 3.5 V. The p.d. across the third is:

  1. 3 V
  2. 1.5 V
  3. 30 V
  4. 6 V

Answer: A) 3 V

Explanation: Kirchhoff's second law: sum V = mathcalE Rightarrow V3 = 9 - 2.5 - 3.5 = 3 V. SLO P-09-E-19 · Understanding

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92. For two resistors in parallel across a 9 V supply, the p.d. across each is:

  1. 9 V
  2. 4.5 V
  3. 18 V
  4. 3 V

Answer: A) 9 V

Explanation: Each forms a loop with the supply. SLO P-09-E-19 · Understanding

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93. A current of 2 A flows for 10 s through a p.d. of 6 V. The energy transferred is:

  1. 240 J
  2. 12 J
  3. 60 J
  4. 120 J

Answer: D) 120 J

Explanation: Q = It = 20 C; W = QV = 120 J. SLO P-09-E-11 · Application

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94. Two branches in parallel across 10 V: branch A has 2 Ω + 3 Ω; branch B has 10 Ω. The total current is:

  1. 2 A
  2. 1 A
  3. 3 A
  4. 0.67 A

Answer: C) 3 A

Explanation: Branch A: 2 A; branch B: 1 A. SLO P-09-E-22 · Application

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95. The principle of the potentiometer is that the p.d. across a length of uniform wire carrying a steady current is:

  1. independent of length
  2. proportional to the square of the length
  3. proportional to the length
  4. inversely proportional to the length

Answer: C) proportional to the length

Explanation: V propto l. SLO P-09-E-23 · Application

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96. A main current of 3 A splits into two branches. One branch carries 1.2 A. The other carries:

  1. 1.8 A
  2. 3.0 A
  3. 4.2 A
  4. 1.2 A

Answer: A) 1.8 A

Explanation: 3 - 1.2. SLO P-09-E-18 · Knowledge

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97. Maximum power is delivered to an external load when R = r. The efficiency then is:

  1. 25%
  2. 50%
  3. 75%
  4. 100%

Answer: B) 50%

Explanation: Half the power is wasted in r. SLO P-09-E-26 · Understanding

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98. A current of 1 A flows in a wire with n = 6 10^28 m^-3 and area 2 10^-7 m^2. The drift velocity of the electrons is:

  1. 5.21 10^-4 m/s
  2. 5.21 10^-5 m/s
  3. 0.00521 m/s
  4. 0.00104 m/s

Answer: A) 5.21 10^-4 m/s

Explanation: v = InAq = 5.21 10^-4 m/s — very slow. SLO P-09-E-10 · Application

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99. If more current entered a junction than left it, charge would:

  1. be destroyed
  2. build up at the junction — which doesn't happen
  3. flow backwards
  4. turn into energy

Answer: B) build up at the junction — which doesn't happen

Explanation: Charge is conserved. SLO P-09-E-18 · Knowledge

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100. A solar cell's e.m.f. comes from converting:

  1. nuclear energy
  2. chemical energy
  3. kinetic energy
  4. light energy into electrical energy

Answer: D) light energy into electrical energy

Explanation: Photovoltaic effect. SLO P-09-E-15 · Application

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