Electricity

1) How does an object become positively charged ?
The object has to lose electrons (leaving more positive charge)

2) How does an object become negatively charged ?
The object has to gain electrons (increasing its negative charge)

3) What is an Electric Field ?
This refers to the area around an object that is affected by an electric force (non contact)
The electric field can be illustrated with a diagram showing arrows.
The direction of the arrow shows the direction a positive charge will be pushed.
It points towards the negative charge.
The closer together the arrows are, the stronger the field.

4) Can electric forces affect the air around them ?
Yes. An object that has an electric force can affect another object without the objects touching.

5) What happens when these two charged objects get close together ?
Positive + Positive - They repel each other.
Positive + Negative - They attract each other.

6) What is Static Electricity ?
When electric charge is not flowing it is called static electricity
When two insulating objects are rubbed together electrons are transferred from one object to the other.

7) What is Electricity ?
This is the name given to the type of energy created when electric current flows through a circuit.
Electricity is the flow (or movement) of electrons in a circuit.
Electric current flows from a power supply in a loop around a circuit and back to the power supply.
Anything that needs electricity to work is called an electrical appliance.

8) What is an Electric Current ?
Electric current is the flow of negative charge (or electrons) around a circuit.
The amount of electrons that are moving is called the current.
Current can only flow if a circuit is complete with no gaps.

9) What is the unit for Electric Charge ?
Coulombs,

Charge Flow (C) = Current (A) x Time (s) 

10) Does an Electric Current generate an electric field ?
Yes.

11) Does an Electric Current generate a magnetic field ?
Yes. You can see this by putting a compass near an electric current.

12) Does current get used up ?
Current is not used up.
The total current is always the same.

13) What is a Battery ?
It contains energy that can be used to transfer chemical energy into an electric current.
A battery provides the force that can push electric charge around a circuit.
A battery will have a potential difference rating
A battery produces DC (direct current) as opposed to AC (alternating current).

14) What is Potential Difference ?
Another word for potential difference is Voltage.
The Potential Difference is the force that pushes the electrons (negative charge) around the circuit.
This is the work done per unit of charge passing between two points.
If you increase the potential difference more current will flow.

15) What is a Transformer ?
A transformer is a device that can change the potential difference or voltage of an alternating current.
A basic transformer is made from two coils of wire, a primary coil from the alternating current (ac) input and a secondary coil leading to the ac output.
The coils are not electrically connected. Instead, they are wound around an iron core.
This is easily magnetised and can carry 'magnetic fields ' from the primary coil to the secondary coil.

16) What are the two different types of transformers called ?
Step Up - Potential Difference increased. Current decreases. Efficient transmission
Step Down - Potential Difference decreased. Current increases.

17) Why is electricity not transmitted with a high current ?
When there is a high current the wires will get extremely hot and a lot of energy will be wasted and transferred to the thermal energy store of the surroundings.

18) What is Resistance ?
Resistance is what slows down the electrons / flow of current.
Resistance is measured in Ohms
The lower the resistance the better the material is at conducting electricity.
Wood has a very high resistance. Metal has a very low resistance.

19) What is a Resistor ?
A resistor is a component that can reduce the current and lower the potential difference in a circuit.
Examples are: LDR, Thermister

20) What are Conductors ?
Conductors are materials that allow electricity to pass through them easily (eg metals)
The lower the resistence the better it is at conducting electricity.

21) What is an Ohmic component (or conductor) ?
These are components that obey Ohm's Law and will always have a constant resistance.
This means the current passing through is directly proportional to the potential difference resulting in the resistance always being constant.
Changing the potential difference or the current will not change the resistance.
For example a resistor.

22) Can you name two components that have a resistance that does change ?
Filament Lamp, Diode

23) What is a Diode ?
A diode is a compoment that allows current to flow easily in one direction but restricts the flow of current in the opposite direction.

24) What are Insulators ?
Insulators are materials that do not allow electricity to pass through them easily (eg wood)

25) What is an Ammeter ?
This is a device used to measure the Current in a circuit.
It is measured in Amperes (A)

26) What is a Voltmeter ?
This is a device used to measure the Potential Difference (or Voltage) in a circuit.
To measure the potential difference you need to measure it between two different points on the circuit.
It is measured in Volts (V)

27) What is a Thermistor ?
This is a temperature dependent resistor.
In hot conditions, the resistance drops.
In cold conditions, the resistance increases.

28) What is a Light Dependent Resistor LDR ?
This is a resistor that is dependent on the intensity of light.
In bright light, the resistance drops.
In dark light, the resistance increases.

29) What is a Filament Lamp ?
A filament lamp is a type of light bulb that produces light by heating a thin wire filament until it glows.
It will tell you the maximum potential difference that you can safely put through it.

30) What happens to the resistance of a filament lamp as the temperature of the filament increases ?
If the temperature of the filament increases this is because more current is flowing through it which increases the resistance.

31) What is a Circuit Diagram ?
A drawing that uses circuit symbols to show all the components in a circuit and how they are connected.
Cell - single energy source
Battery - multiple energy sources
Switch - these can be switches on or off, when off, the switch is open
Bulb - device that produces light from an electric current
Buzzer -
Voltmeter - an instrument measuring the volts
Ammeter - an instrument measuring the amps

32) What is a Series Circuit ?
There is only one route that the current can take
The total potential difference is shared between all the components.
The potential difference around a series circuit always adds up to the source potential difference.

33) What happens to the current if you increase the resistance ?
The current would decrease.

34) What is the current passing through two resistors of 2 and 3 ohms if the potential difference is 20 volts

Potential Difference = Current x Resistance 

Current = 20 / (2 + 3)
Current = 4 amps

35) What is a Parallel Circuit ?
There is more than one route that the current can take.
The current is shared. It may not be the same everywhere.
The potential difference is not shared. It is the same on both branches.

36) What happens when you add resistors in parallel ?
The total resistance decreases.
The potential difference is the same and because PD = Current x Resistance
The current increases.

37) What are the three different wires that most electrical appliances have ?
Brown - Live
Blue - Neutral
Green / Yellow - Earth

38) What is the Potential Difference or Voltage in most UK homes ?
An AC (alternating current) of around 230 volts.

Electricity Questions