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Electricity, magnetism and circuits
7 NET Physics questions with answers and explanations.
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Inside a conductor in electrostatic equilibrium, the electric field is:
- 1 Maximum
- 2 Zero
- 3 Equal to the field outside
- 4 Infinite
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Correct answer: Zero
If a field existed, charges would move. In equilibrium the charges have settled so that the field inside is zero.
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Kirchhoff's junction rule is based on the conservation of:
- 1 Energy
- 2 Momentum
- 3 Charge
- 4 Mass
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Correct answer: Charge
The current entering a junction equals the current leaving it, because charge cannot build up there.
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A charged particle moves at right angles to a uniform magnetic field. If its speed is doubled, the radius of its circular path:
- 1 Halves
- 2 Doubles
- 3 Stays the same
- 4 Becomes four times as large
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Correct answer: Doubles
The radius is mv / qB, so it is proportional to the speed.
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The peak voltage of an AC supply is 311 V. What is its approximate rms value?
- 1 311 V
- 2 220 V
- 3 155 V
- 4 440 V
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Correct answer: 220 V
V_rms = V_peak / sqrt(2) = 311 / 1.414, which is about 220 V.
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What is the inductive reactance of a 0.1 H inductor at 50 Hz? (Take pi = 3.14)
- 1 5 ohm
- 2 314 ohm
- 3 31.4 ohm
- 4 3.14 ohm
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Correct answer: 31.4 ohm
X_L = 2 pi f L = 2 x 3.14 x 50 x 0.1 = 31.4 ohm.
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An ideal ammeter should have:
- 1 Very high resistance
- 2 Zero resistance
- 3 Resistance equal to the circuit
- 4 Infinite capacitance
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Correct answer: Zero resistance
An ammeter is connected in series and should not disturb the current, so its resistance should be as close to zero as possible.
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The SI unit of self-inductance is the:
- 1 Weber
- 2 Tesla
- 3 Henry
- 4 Farad
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Correct answer: Henry
Inductance is measured in henry. The weber is for magnetic flux and the tesla for magnetic field.