Current Electricity
14 free MDCAT Physics MCQs on Current Electricity (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.
Tap an answer to check it · 14 questions
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Question 1
The drift velocity of charge carriers per unit electric field is their:Show answer and explanation
Answer: D) Mobility
Mobility = v/E. Source: 11 Physics Book FBISE, p. 199.
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Question 2
A null-type resistance network device used for measuring potential differences is a:Show answer and explanation
Answer: C) Potentiometer
An unknown emf is balanced against a known potential difference. Source: 11 Physics Book FBISE, p. 212.
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Question 3
It takes 600 J of energy to move a charge of 2 C between two points in an electric field. The potential difference between them is:Show answer and explanation
Answer: A) 300 V
V = W/q = 600/2 = 300 V. Source: 11 Physics Book FBISE, p. 202.
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Question 4
A 2 V emf source has internal resistance 0.02 ohm. If its terminals are joined directly to each other, the current is:Show answer and explanation
Answer: B) 100 A
I = E/r = 2/0.02 = 100 A. Source: 11 Physics Book FBISE, p. 218.
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Question 5
A copper coil has 2000 turns of 80 cm each, wire cross-section 0.8 mm2 and resistivity 0.02 micro-ohm m. Its resistance is:Show answer and explanation
Answer: C) 40 ohm
R = rho L/A = 0.02e-6 x 1600 / 0.8e-6 = 40 ohm. Source: 11 Physics Book FBISE, p. 218.
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Question 6
Compared with the drift velocity, the average Fermi velocity of electrons in a metal is:Show answer and explanation
Answer: D) Very high
Fermi velocity is about 10^6 m/s; drift velocity about 10^-3 m/s. Source: 11 Physics Book FBISE, p. 198.
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Question 7
In the absence of an external electric field, the free electrons in a metal:Show answer and explanation
Answer: A) Move randomly with no net drift
An external field is needed for a net drift current. Source: 11 Physics Book FBISE, p. 198.
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Question 8
Despite its name, electromotive force actually represents:Show answer and explanation
Answer: B) Work per unit charge
Its unit is the volt, the same as potential difference. Source: 11 Physics Book FBISE, p. 202.
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Question 9
A cell acting as a source of emf converts:Show answer and explanation
Answer: C) Chemical energy into electrical
The emf drives charges around the circuit. Source: 11 Physics Book FBISE, p. 202.
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Question 10
The resistance of a wire is directly proportional to its:Show answer and explanation
Answer: D) Length
R = rho L / A. Source: 11 Physics Book FBISE, p. 203.
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Question 11
A wire of resistance R is replaced by one of the same length and material but double the cross-sectional area. The new resistance is:Show answer and explanation
Answer: A) R/2
R is inversely proportional to the area. Source: 11 Physics Book FBISE, p. 204.
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Question 12
Unlike resistance, resistivity is an intrinsic property, so it does not depend on the conductor's:Show answer and explanation
Answer: B) Physical dimensions
Resistance depends on length and area; resistivity on the material. Source: 11 Physics Book FBISE, p. 204.
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Question 13
Kirchhoff's current law (first law) is a statement of the law of conservation of:Show answer and explanation
Answer: A) Charge
Charge entering a junction must leave it. Source: 11 Physics Book FBISE, p. 208.
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Question 14
When a Wheatstone bridge is balanced, the galvanometer:Show answer and explanation
Answer: A) Reads zero
Points B and D are then at the same potential, and P/Q = R/S. Source: 11 Physics Book FBISE, p. 212.
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