 # Electricity calculations

1.         Copy and complete this table:

 Potential difference Current Resistance 10V 5A 12V 3A Mains 10A 20kV 50A 10V 100ohms 9V 10Kohms 1.8mA 2.2kohms

2.         If a resistor has a resistance of 200ohms calculate the voltage required to cause a current of 100mA to flow

3.         Repeat for a resistance of 200lohms and a current of 20Amperes

4.         A 300kohm resistor has 1A flowing through it.  What is the p.d. across it? 5.

(a)        Write down the current flowing through R1

(b)        Calculate the resistance of R1

(c)        Calculate the p.d. across R2

(d)        Calculate the resistance of R2

(e)        Write down all the scientific principles that this question relies upon.

6.         What is the power of an appliance that passes 200J of energy in 4 seconds

7.         What is the power of an electric iron that passes 600kJ in 14 minutes?

8.         What is the power of an electric kettle that uses mains electricity passes a current of 3A?

9.         A fluorescent light bulb passes a current of 150mA when connected to the mains.  What is its power rating?

10.        What is the current passed through a colour tv rated at 340W that is connected to the mains?

11.        Why would it be wrong to use a 5A fuse in an immersion heater rated at 3000W (connected to the mains)?

12.        Why would it be wrong to use a 13A fuse in a table lamp rated at 60W when connected to the mains supply?

13.       A 3kW electric fire is used for 10 minutes.  (a) Calculate the Joules of electricity that it converts.  (b) What energy is the electricity converted into?

** 14.    What is the resistance of a mains powered electric fire rated at 1kW?

** 15.    An electric light bulb, rated at 100W, has a resistance of 26 ohms.   Calculate the voltage of the power supply.

16.       A dishwasher has a resistance of 19 ohms.  Calculate the energy converted by the dishwasher during a half hour cycle if used at mains voltage?

17.       Calculate the kWhours of electricity consumed by a 2kW electric fire in 2 hours.

18.       If 1 unit of electricity costs 7p (1kWhr = 7p) calculate the cost of using an immersion heater rated at 4000W for 10hours.

** 19.    Calculate the resistance of an electric kettle if it costs 16.8p per hour to run it on mains power. (Take 1 unit = 7p)

20.       An office has five 60W bulbs, a 2kW electric fire and a 200W computer.  Calculate the maximum electricity costs of  this office per 24 hours period.  (Take 1 unit = 7p)