The table below shows the current in three different electrical appliances when connected to the 240 V mains supply :
Appliance current
Kettle 8.5 A
Lamp 0.4 A
Toaster 4.8 A
(a) Which appliance has the greatest electrical resistance ? How does the data show this ?
(b) The lamp is connected to the mains supply by using a thin, twin-cored cable consisting of live and neutral wires. State two reasons why this cable should not be used for connecting the kettle to the mains supply.
(c) Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
(d) A man takes the kettle abroad where the mains supply is 120 V. What is the current in the kettle when it is operated from the 120 V supply ?
The table below shows the current in three different electrical appliances when connected to the 240 V mains supply :
Appliance current
Kettle 8.5 A
Lamp 0.4 A
Toaster 4.8 A
(a) Which appliance has the greatest electrical resistance ? How does the data show this ?
(b) The lamp is connected to the mains supply by using a thin, twin-cored cable consisting of live and neutral wires. State two reasons why this cable should not be used for connecting the kettle to the mains supply.
(c) Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
(d) A man takes the kettle abroad where the mains supply is 120 V. What is the current in the kettle when it is operated from the 120 V supply ?
(a) For a given potential difference, the amount of current the appliance draws, can give us an idea of the resistance of the appliance
as current is inversely proportional to the resistance hence we can say that the more the reisstance the less the current drawn.
So the greatest electrical resistance is of the lamp.
(b)
- Even though the current through lamp is smallest in the group, but it is quite large, so Earthing is necessary. Hence twin chord cable should not be used.
- In general, earthing should be done in every heavy duty device.
(c) Power (P) = V x I = 240 x 8.5 = 2040
(d) Since, the resistance is contant and the voltage is reduced to half, and current is directly proportional to Voltage, hence the current will also be reduced to half, so it will become 4.25A.
(a) For a given potential difference, the amount of current the appliance draws, can give us an idea of the resistance of the appliance
as current is inversely proportional to the resistance hence we can say that the more the reisstance the less the current drawn.
So the greatest electrical resistance is of the lamp.
(b)
- Even though the current through lamp is smallest in the group, but it is quite large, so Earthing is necessary. Hence twin chord cable should not be used.
- In general, earthing should be done in every heavy duty device.
(c) Power (P) = V x I = 240 x 8.5 = 2040
(d) Since, the resistance is contant and the voltage is reduced to half, and current is directly proportional to Voltage, hence the current will also be reduced to half, so it will become 4.25A.
