Mains Electricity
4 marks · EasyA desk lamp is powered by batteries providing direct current (d.c.). A television is powered from the mains (a.c.) supply.
State the difference between the current supplied by batteries and the current supplied by the mains.
Explain why a fuse is used in the plug of the television.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Batteries provide direct current (d.c.), which flows in one direction only; mains supply provides alternating current (a.c.), which changes direction repeatedly. · must show d.c. one direction, a.c. changes direction
(b) A fuse is used to protect the television and user. If too large a current flows, the fuse melts and breaks the circuit, preventing damage and reducing the risk of fire or electric shock. · must show Fuse melts with too much current, Prevents electric shock/damage/fire
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that batteries provide d.c. (direct current) which flows in only one direction.
B2 (a) · 1 mark · States that mains provides a.c. (alternating current) which reverses direction repeatedly.
B3 (b) · 1 mark · Explains that the fuse melts or 'blows' if the current is too large.
B4 (b) · 1 mark · Explains that this stops current, protecting the appliance and user from damage or electric shock/fire.
Worked solution
(a) The current from batteries is direct current (d.c.), which flows in one direction only. The current from the mains is alternating current (a.c.), which changes direction repeatedly.
(b) A fuse is used so that if too much current flows, it will melt and break the circuit. This prevents damage to the television, reduces the chance of fire, and protects the user from electric shock.