Basic Electric Circuits Questions and Answers

The answers have been provided towards the end of these questions:

1. If a current of 10 A flowing for 2 minutes, find the quantity of electricity transferred.
2. A mass of 5000 g is accelerated at 2 m/s² by a force. Determine the force required.
3. A typical 12 V automobile battery, storing about 5 megajoules (MJ) of energy, is connected to a 4 A headlight system. (a) Find the power delivered to the headlight system (b) Calculate the energy consumed in 1 hour of operation (c) Express the auto-battery capacity in ampere-hours (Ah) and compute how long the headlight system can be operated before the battery is completely discharged.
4. A mass of 1000 kg is raised through a height of 10 m in 20 s. Calculate:(a) The work done (b) The power developed.
5. Find the conductance of a conductor of resistance 100 ꭥ
6. A source of e.m.f of 10 V supplies a current of 3 A for 10 minutes. How much energy is provided in this amount of time?
7. An electric heater consumes 1.8 MJ when connected to a 250 V supply for 30 minutes. Find the power rating of the heater and the current taken from the supply.
8. If a current of 20 A flows for 10 minutes find the quantity of electricity transferred.
9. The current flowing through a resistor is 0.8 A when a voltage of 200 V is applied. Calculate the value of the resistance.
10. A 100 V battery is connected across a resistor and causes a current of 5 mA to flow. Determine the resistance of the resistor. If the voltage is reduced to 25 V, what will be the new value of the current flowing?

Answers:

1. Quantity of electricity Q =1200
2. Force = 10 N
3. (a) Power = 48 W, (b) assuming V & I remain constant, the energy consumed in 1 hour, W = 48 (60×60) = 172.8 x 10³ J = 172.8 KJ, (c) hint 1 Ah =  = 3600 C, [ energy = VIt) but It = Q,  therefore, charge Q =  = J = 0.417 x 10⁶ C, thus the auto-battery capacity is , without completely discharging the battery, the headlight system can be operated for   = 29
4. (a) Work done = 98.1 KJ or 98.1 kNm, (b) Power = 4905 W or 4.905 KW
5. Conductance (G) = 0.01 s
6. Energy = VIt = 10 x 3 x (10 x 60) = 18000w or 18 KJ
7. Power rating of the heater = 1 kW, current taken from the supply is 4 A
8. Quantity of electricity Q = 2400 C
9. Resistance (R) = 250 ꭥ
10. Resistance R = 20 kꭥ, current when the voltage is reduced to 25 V = 1.25 mA