P2 - Electricity Flashcards
What is the frequency of the mains electricity supply in the UK?
50Hz
Give an advantage of using a RCCB to switch off a circuit rather than a fuse.
Faster acting, can be reset
How does an increase in temperature affect a thermistor?
Increase in temperature decreases resistance of thermistor
What is the difference between ac and dc current?
The dc flows in one direction, the ac changes direction twice per cycle
How do a fuse and the earth wire protect against an electric shock in a faulty metal kettle where the metal casing becomes live?
A current flows from the live wire to the earth wire and this current causes the fuse to melt
Describe the structure of a cable that is used to connect a hob to the mains electricity supply.
cable must contain a live, neutral and earth wire and should be insulated with plastic
Define electric current.
Flow of charge/ electrons
Define potential difference.
work done or energy transferred per coulomb of charge V= W/Q
Why does the resistance of a light bulb increase with p.d.?
Metals contain ions and free electrons. As temperature increases, ions vibrate faster and the electrons collide more often with the ions so their velocity decreases
Why is it dangerous to use a piece of aluminium as a fuse?
A large current will flow through aluminium metal but the aluminium will not melt so the wiring in the appliance might overheat and cause a fire
Why do your hairs stand on end when you are connected to the Van de Graaff generator?
Because each hair has the same negative charge and negative charges repel
What name is given to the rate of flow of charge?
Current
Explain why it is a good idea for electricians to wear boots with rubber soles.
Rubber is a good insulator and it increases the overall resistance so gives a smaller shock
From a safety point of view, is 50Hz a suitable frequency?
No, as this frequency is the lowest current at which people cannot let go. Or Yes, changing the frequency changes the current only by a small amount.
Fine powders poured through a pipe can become negatively charged. How?
Friction between powder and pipes causes electrons to transfer from the pipe to the powder
Place a charged rod on an insulated balance. Take a second charged rod and hold it above the rod on the balance. The reading on the balance increases. Why?
The two rods repel, creating a downwards force on the rod that is placed on the balance
Define double insulated.
The case of an appliance is made of plastic and there is no connection between the inner and outer insulated parts of the appliance.
How do you calculate the total resistance of two resistors in series?
Addition of both resistance values
What is the mains pd in the UK?
230V
What are the colours of the live, earth and neutral wire inside a 3 pin plug?
Live is brown, earth is yellow and green and neutral is blue
An appliance requires 5A. What size fuse do you use-1,3, 5 or 13A?
13A
How does the resistance of an LDR change with light intensity?
The higher the light intensity the lower the resistance
How does a spray gun work which is used to cover car panels in paint?
Each paint droplet is given the same charge so the droplets repel. The car panels are given the opposite charge. The droplets are attracted to the panels and cover the panels evenly
In a parallel circuit the potential difference across each component is…..
The same
In a series circuit the potential difference of the power supply is….
Shared by the components
Draw a current-voltage graph for a diode.
Draw a current-voltage graph for a filament lamp.
Draw a current-voltage graph for a metal wire.
People working with computer chips are required to wear a special bracelet that is attached to a wire that joins to earth. Why?
So that any negative charge that builds up on the person can flow through the wire to earth.
What is the circuit symbol for a diode?
What is the circuit symbol for a variable resistor?
What is the circuit symbol for a thermistor?
What is the circuit symbol for an LDR?
What is the circuit symbol for an LED?
Where would you find a thermistor inside your home?
inside a thermostat to control the heating
Which type of resistor is found in a circuit that automatically switches on lights when it gets dark?
An LDR
