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Solved problems for the chapter:

Electrical Power

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Electric Power for A-Levels

1. Electrical work

2. Electrical power

3. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:electrical_power/5121/

Example 1.

A household consumes 100 kW h of electrical energy per week.

What is the average connection power of all consumers in the household?
What is the average current if the mains voltage is 230 V?

Example 2.

What is the total power consumable from a source with a voltage of 220 V and a fuse rated 25 A.

Two resistors with resistances and are connected in parallel to a 120 V voltage source.

Calculate the power dissipated by each of the two resistors.
Calculate the power output of the voltage source.

A current of 6 mA flows through a resistor with a resistance . How much power does the resistor receive?

The graph of the voltage against the current for a bulb is given below.

What is the power of the bulb at 50 V?
What is the power of the bulb at a nominal voltage of 220 V?

A voltage of 60 V is connected to two resistors of resistances and which are in series.

What is the power of each of the resistors?
What is the total power of both resistors?

Two resistors with resistances and are connected in series to a 220 V voltage source.

Calculate the power dissipated by each of the two resistors.
Calculate the power output of the voltage source.

Two identical 60 W bulbs are connected in parallel first and then in series to the 220 V mains.

What is the power dissipated by each bulb and the total power dissipated by the bulbs in the case of a parallel connection?
What is the power dissipated by each bulb and the total power dissipated by the bulbs in the case of a series connection?

Assume that the resistance of the bulbs does not change.

A bulb has a power of 80 W at a voltage of 230 V. What is its resistance?

10.

What is the maximum number of identical bulbs with a voltage of 10 V that we need to connect in series to a voltage source of 220 V?
What will be the total power of the bulbs if the power of each bulb is 4 W?

11.

A household has a dishwasher with a power of 3 kW and an electric stove with a power of 2 kW connected to the same fuse. The mains voltage is 230 V. We have 10, 15, 20 and 25 A fuses available. Which should we use to protect the circuit if both devices can be connected at the same time?

12.

A car battery has a voltage of 12 V and a charge of 60 Ah. How long will it take to discharge if we leave a 6 W light bulb on?

13.

There is a current in a resistor of resistance for a time . The potential difference (p.d.) across the resistor is . Which equation gives the power dissipated in the resistor?