Electricity, magnetism and circuits

Written by Dr. Hamza Farooq (Physics)

NET · Physics · 7 questions

Name: ____________________ Date: ____________

Inside a conductor in electrostatic equilibrium, the electric field is:
- A Equal to the field outside
- B Zero
- C Maximum
- D Infinite
Kirchhoff's junction rule is based on the conservation of:
- A Charge
- B Momentum
- C Mass
- D Energy
A charged particle moves at right angles to a uniform magnetic field. If its speed is doubled, the radius of its circular path:
- A Stays the same
- B Becomes four times as large
- C Halves
- D Doubles
The peak voltage of an AC supply is 311 V. What is its approximate rms value?
- A 155 V
- B 311 V
- C 220 V
- D 440 V
What is the inductive reactance of a 0.1 H inductor at 50 Hz? (Take pi = 3.14)
- A 314 ohm
- B 3.14 ohm
- C 5 ohm
- D 31.4 ohm
An ideal ammeter should have:
- A Resistance equal to the circuit
- B Very high resistance
- C Infinite capacitance
- D Zero resistance
The SI unit of self-inductance is the:
- A Henry
- B Farad
- C Tesla
- D Weber

Answer key

1. B, 2. A, 3. D, 4. C, 5. D, 6. D, 7. A

If a field existed, charges would move. In equilibrium the charges have settled so that the field inside is zero.
The current entering a junction equals the current leaving it, because charge cannot build up there.
The radius is mv / qB, so it is proportional to the speed.
V_rms = V_peak / sqrt(2) = 311 / 1.414, which is about 220 V.
X_L = 2 pi f L = 2 x 3.14 x 50 x 0.1 = 31.4 ohm.
An ammeter is connected in series and should not disturb the current, so its resistance should be as close to zero as possible.
Inductance is measured in henry. The weber is for magnetic flux and the tesla for magnetic field.