10 minutes maximum! Can you do it in 5?

1. Which of these gives the formula for calculating electrical power?

• A. power = current x charge
• B. power = current x voltage
• C. power = voltage x resistance
• D. power = voltage x charge
2+3. A student is comparing power banks to take on holiday.
The output of the most powerful one is 5V at 2.4 A maximum.

2. What is the maximum power output of this power bank?

• A. 2.1 W
• B. 0.48 W
• C. 12 W
• D. 4.8 W

3. A different power bank has a lower power output. If the voltage output is still 5V, how does this affect the current output and the energy transferred per second, compared to the first power bank?

current energy transferred per second
A
lower lower
B
lower same
C
same lower
D
same same

4-6: The table below gives some information about 3 different cells. What are the missing values?

 voltage max. current power 4. 1.5 V 0.2 ? 7.5 W 75 W 3 W 0.3 W 5. ? 0.1 V 1 V 10 V 100 V 100 mA 1 W 6. 6 V ? 0.05 mA 50 mA 1.8 mA 1800 mA 300 mW

7-9: An electric kettle is rated as 240 V, 2 kW.

7. What is the current used when switched on?

• A. 120 A
• B. 480 A
• C. 0.12 A
• D. 8.3 A

8. Which of the following gives the correct formula to calculate the electrical energy transferred to the kettle?

• A. E = I x V x t
• B. E = I x V x R
• C. E = I x R x t
• D. E = R x V x t

9. The kettle takes 2 minutes to boil. How much electrical energy has been used to heat the water?

• A. 1 kJ
• B. 4 kJ
• C. 16 J
• D. 240 kJ

10. The power bank in question 2 has an output of 5 V and a maximum current of 2.4 A. If it can last for 50 minutes before running out, what energy is stored in the power bank?

• A. 3000 J
• B. 600 J
• C. 6000 J
• D. 36 000 J