12th grade electricity and magnetism

Question 1

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 2

Two small charged spheres carry 5 µC and 1 µC and are 0.5 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 3

What does a step-down transformer near your home do?

• A. increases the voltage for homes
• B. reduces the voltage to a safer level, about 230 V in the UK
• C. turns ac into dc
• D. stores electricity for the night

Question 4

One charge is multiplied by 2 and the distance is unchanged. By what factor does the force change?

Answer 

Question 5

How is the electrostatic force different from gravity?

• A. It only acts on metals
• B. It can attract or repel; gravity only attracts
• C. It does not depend on distance
• D. It is always weaker

Question 6

A 100 % efficient transformer has an input of 230 V and 5 A. The output voltage is 115 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 7

A transformer has 100 turns on the primary coil and 1000 turns on the secondary. The input voltage is 120 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 8

A 10 Ω resistor is in series with a parallel pair of 10 Ω and 15 Ω. The supply is 8 V. What current flows from the supply, in A?

Answer A

Question 9

Three resistors of 10 Ω, 15 Ω and 1 Ω are connected in series. What is the total resistance, in Ω?

Answer Ω

Question 10

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

Answer Ω

Question 11

Two small charged spheres carry 3 µC and 2 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

Question 12

What does a step-down transformer near your home do?

• A. stores electricity for the night
• B. increases the voltage for homes
• C. reduces the voltage to a safer level, about 230 V in the UK
• D. turns ac into dc

Question 13

The distance between two charges is multiplied by 4. By what factor does the electrostatic force change? (Give 4 decimal places.)

Answer 

Question 14

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

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

Question 15

A 100 % efficient transformer has an input of 400 V and 10 A. The output voltage is 46 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 16

A transformer has 200 turns on the primary coil and 400 turns on the secondary. The input voltage is 400 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V