P2- Electricty

Question 1

The total charge through a circuit depends on what?

Answer 1

Current and time.

Question 2

What’s the units for current?

Answer 2

Amphs (A)

Question 3

What’s the formula linking potential difference and current?

Answer 3

V= IR

Question 4

What does ohmic conductors have?

Answer 4

Ohmic conductors have a constant resistance.

Question 5

What’s the Investigating resistance practice?

Question 6

Describe what the graph will look like for an ohmic conductor?

Answer 6

1. Current is directly proportional to the potential difference
2. So you get a straight line.

Question 7

Describe what the graph for a filament lamp will look like.

Answer 7

1. Temperature increases as current increases.
2. So resistance increases.
3. This makes it harder for current to flow.
4. So the graph gets less steep.

Question 8

Describe what the graph for a diode will look like.

Answer 8

1. Current only flows in one direction.
2. The diode has very high resistance in the reverse direction

Question 9

What is LDS?

Answer 9

Light dependent resistors

Question 10

What can sensing circuits be used for?

Answer 10

Sensing circuits can be used to automatically change the pd across components depending on charges in the environment.

Question 11

Describe a series circuit.

Answer 11

1. In a series circuit, the components are all connected in a line between the ends of the power supply
2. Voltmeters are always parallel
3. If you remove one component, the circuit is broken so all the components stop working.
4. In series the total od of the supply is hared between all the components.
5. In series circuits the same current flows through all components.
   ( in series the total resistance of two components is found by adding up their resistances).

Question 12

Explain why adding resistors in series increases the total resistance of the circuit.

Answer 12

1. Adding a resistor in series means the resistors have to share the total pd.
2. This means that the pd across each resistor is lower, so the current through each resistor is lower
3. The current is the same everywhere
4. So the total current in the circuit is reduced when a resistor is added
5. This means the total resistance of the circuit has gone up.

Question 13

Describe a parallel circuit.

Answer 13

1. In a parallel circuit , each component is separately connected to the ends of the power supply.
2. Ammeters are always in series
3. If you take out one of the loops in the parallel circuit, the things in the other loops won’t be affected.
4. This means things in parallel can be switched on and off without affecting eachother
5. In parallel circuits all components get the full source of pd
6. So the potential difference is the same across all components

Question 14

Why does adding a resistor in parallel reduce the total resistance?

Answer 14

1. If you add a resistor in parallel, both resistors still have the same potential difference across them as the power supply.
2. This means the ‘pushing force’ making the current flow is still the same.
3. But by adding another loop, the current has more than one direction to go in.
4. More current can flow around the circuit so the total current increases.
5. This means the total resistance of the circuit is lower.

Question 15

What’s the practice for investigating circuits?

Question 16

What are the 3 wires in most cables?

Answer 16

Live wire.
Neutral wire.
Earth wire.

Question 17

What colour is the live wire?

Answer 17

Brown

Question 18

What colour is the neutral wire?

Answer 18

Blue

Question 19

What is the colour of the earth wire?

Answer 19

Green and yellow

Question 20

What is the function of the live wire?

Answer 20

The live wire provides the alternating potential difference form the mains supply.
(It is about 230V)

Question 21

What is the function of the neutral wire?

Answer 21

The neutral wire completes the circuit
- when the appliance is operating normally current flows through the live and neural wires.
(It is about 0V)

Question 22

What is the function of the earth wire?

Answer 22

The earth wire is a safety wire.
It stops the appliance becoming live.
It is connected to the metal casing of an appliance
If a fault causes the live wire to touch the casing the current flows away through the earth wire.
(It’s also at 0V)

Question 23

Why can the live wire give you an electric shock?

Answer 23

1. There is a pd between the live wire and your body (which is at 0V)
2. Touching the live wire can cause a current to flow through your body.
3. This can give you a dangerous electric shock.
4. Even if a switch is turned off ( the switch is open), touching the live wire is still dangerous.
5. This is because it still has a pd of 230V.
6. Any connection between the live and earth can be dangerous.
7. The pd could cause a huge current to flow which could result in a fire.

Question 24

Explain what happens when a energy is transferred in a circuit?

Answer 24

1. When a charge moves around a circuit, work is done against the resistance of the circuit.
2. Whenever work is done, energy is transferred.
3. When the work is done by the charge, the energy is transferred electrically.
4. Electrical appliances transfer energy to components in the circuit when a currency flows.

Question 25

How is electricity distributed?

Answer 25

Through the national grid.

Question 26

What does the national grid do?

Answer 26

Distributes energy.
- transfers electrical power from power stations to consumers.

Question 27

What are step-up transformers used for?

Answer 27

Step-up transformers are used to increase the pd from power stations to electric cables.

Question 28

What are step-down transformers used for?

Answer 28

Step-down transformer bring the pd of back down to safe levels before electricity gets to home.