P4c - Safe Electricals Flashcards
What are resistors used for?
What is different about variable resistors?
Resistors can be used to slow the flow of current.
Variable resistors change the current by different amounts.
Fill in the blanks.
Long wires have ______ resistance than short wires.
Thin wires have ______more resistance than fat wires.
More.
More.
Fill in the blanks.
The ______ the length of resistance wire connected into the circuit, the ______ the resistance and the ______ the current.
Longer.
Bigger.
Smaller.
Give an example of a variable resistor.
A dimmer switch.
What is the equation for resistance (ohm’s law)?
Resistance = voltage/current
What are voltage, current and resistance each measured in?
Volts.
Amps.
Ohms.
Fill in the blanks.
If the resistance is constant, increasing the voltage will _______ the current.
If the voltage is kept constant, increasing the resistance will _______ decrease the current.
Increase.
Decrease.
What are the 3 cables used in domestic wiring? What do they do? What colour are they?
Live (brown) - carries the high voltage.
Neutral (blue) - completes the circuit.
Earth (green and yellow) - stops appliances becoming live.
Why is an earth wire needed and what does it do?
It makes a connection with something metal in the ground, so if the casing of the appliance becomes live, the charge can flow through the earth wire so the user does not get electrocuted. When a fault causes current to flow through the earth wire, the current is large enough to melt the fuse and break the circuit.
Give an example of when you don’t need to use an earth wire and why?
When the casing of the appliance is plastic, which acts as a second layer of insulation because it does not conduct electricity.
What does a fuse do?
A fuse melts if a fault causes the current to be too large. It breaks the circuit, thus preventing the flex from overheating and causing a fire. It prevents further damage to an appliance.
What are the correct ratings of fuses?
Why must the correct ones be used?
3A, 5A and 13A.
It the current is too large, and you use too small of a fuse, then it will melt all the time and therefore will not work. If she to big of a fuse, then it would not offer as much protection because it won’t melt, even if the current is dangerously large.
How do you calculate current?
Current = power/voltage
What is the difference between a circuit breaker and a fuse?
A circuit breaker can be reset, whereas a fuse has to be replaced.
What are the features of a parallel circuit, compared to a series circuit?
In a parallel circuit you can turn bulbs on and off separately, and if one bulb stops working, the others still work. In comparison, in a series circuit, if one bulb breaks it doesn’t work and the bulbs are dimmer.
