12th grade electricity and magnetism

Question 1

A 12 Ω resistor and a 4 Ω resistor are connected in parallel. What is their combined resistance, in Ω? (1/R = 1/R₁ + 1/R₂)

Answer Ω

Question 2

A transformer has more turns on its secondary coil than its primary coil. What type is it?

• A. a motor
• B. step-down
• C. step-up
• D. a generator

Question 3

A transformer has 100 turns on the primary coil and 10 turns on the secondary. The input voltage is 230 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 4

How is Coulomb's law similar to Newton's law of gravitation?

• A. Both depend on mass
• B. Both are unaffected by distance
• C. Both are inverse square laws
• D. Both forces are always attractive

Question 5

Three resistors of 5 Ω, 3 Ω and 5 Ω are connected in series. What is the total resistance, in Ω?

Answer Ω

Question 6

A 100 % efficient transformer has an input of 230 V and 5 A. The output voltage is 23 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 7

Two small charged spheres carry 1 µC and 3 µC and are 0.1 m apart. What is the size of the force between them, in N? (F = k q₁ q₂ ÷ r², k = 8.99 × 10⁹ N m²/C², 1 µC = 10⁻⁶ C; give 2 decimal places)

Answer N

Question 8

A 10 Ω resistor is in series with a parallel pair of 10 Ω and 15 Ω. The supply is 32 V. What current flows from the supply, in A?

Answer A

Question 9

Both charges are multiplied by 2 and the distance is unchanged. By what factor does the force change?

Answer 

Question 10

A 10 Ω resistor and a 15 Ω resistor are connected in parallel. What is their combined resistance, in Ω? (1/R = 1/R₁ + 1/R₂)

Answer Ω

Question 11

Why does the National Grid transmit electricity at very high voltages?

• A. A high voltage means a low current, so less energy is lost heating the cables
• B. High voltage makes electricity travel faster
• C. Homes need very high voltages
• D. It makes the cables lighter

Question 12

A transformer has 400 turns on the primary coil and 1600 turns on the secondary. The input voltage is 120 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 13

How is Coulomb's law similar to Newton's law of gravitation?

• A. Both are unaffected by distance
• B. Both forces are always attractive
• C. Both are inverse square laws
• D. Both depend on mass

Question 14

Three resistors of 20 Ω, 6 Ω and 2 Ω are connected in series. What is the total resistance, in Ω?

Answer Ω

Question 15

A 100 % efficient transformer has an input of 400 V and 2 A. The output voltage is 23 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 16

Two small charged spheres carry 2 µC and 3 µC and are 0.3 m apart. What is the size of the force between them, in N? (F = k q₁ q₂ ÷ r², k = 8.99 × 10⁹ N m²/C², 1 µC = 10⁻⁶ C; give 2 decimal places)

Answer N