P4 - Electric Circuits

Question 1

What is current?

Answer 1

The flow of electrical charge

Question 2

What is the unit for current?

Answer 2

Amperes (A)

Question 3

What conditions are compulsory for electrical charge to flow around a circuit?

Answer 3

The circuit needs to be complete
There is a source of potential difference

Question 4

What is potential difference?

Answer 4

The driving force that pushed the charge around the circuit

Question 5

What is potential difference measured in?

Answer 5

Volts (V)

Question 6

What is Resistance?

Answer 6

Anything that slows the flow in the current down

Question 7

What is the unit for resistance?

Answer 7

Ohms

Question 8

What is the relationship between resistance and current in a circuit?

Answer 8

The greater the resistance across a component, the smaller the current that flows

Question 9

What is Charge flow measured in?

Answer 9

Coulombs (C)

Question 10

What is the equation that links charge flow, current and time?

Answer 10

Charge flow = current x time

Question 11

What is the formula linking potential difference and current? (Ohms law)

Answer 11

V = IR

Question 12

What does the ammeter measure and what does the voltmeter measure?

Answer 12

Current (amps)
Potential difference (volts)

Question 13

If the resistance is kept constant and the potential difference is increased, what will haooen to the current?

Answer 13

It should increase proportionally

Question 14

What happens when you increase the temperature of a circuit?

Answer 14

The resistance will increase

Question 15

What are diodes?

Answer 15

Devices that only allow current to flow in one direction

Question 16

What does LDR stand for?

Answer 16

Light Dependent Resistor

Question 17

What is a LDR (light dependent resistor?

Answer 17

A resistor with resistance that depends on light intensity

Question 18

What is a thermistor?

Answer 18

A temperature dependent resistor

Question 19

What happens to the resistance of an LDR in Bright light and darkness?

Answer 19

Bright light - resistance is low
Darkness - resistance is high

Question 20

What happens to the resistance in a thermistor in hot and cool conditions?

Answer 20

Hot - the resistance drops
Cool - the resistance increases

Question 21

What is the main difference between a series and a parallel circuit

Answer 21

A series circuit has only one single loop while a parallel circuit has more than 1 loop

Question 22

Why are parallel circuits generally more reliable than series circuits?

Answer 22

If any loop in a parallel circuit breaks, the circuit can still flow

Question 23

How do you carry out the resistance practical?

Answer 23

1. Attach a wire to a meter ruler using tape and connect the wire to the circuit using crocodile clips
2. Move the crocodile clips to the 30cm mark
3. Record the voltage of the battery/cell and use the ammeter to find the current.
4. Find the resistance using V=IR
5. Repeat this, moving the crocodile clip up in 10cm until you get to 100cm
6. Plot the data on a graph

Question 24

What is the ‘National Grid’?

Answer 24

The giant network of transformers and wires that spreads across the country to distribute electricty

Question 25

Where does most of the UKs electricity come from?

Answer 25

Power stations

Question 26

How do power stations generate electricity?

Answer 26

Fuel is burned to heat water to produce steam This steam spins the turbine The turbine drives a generator which produces electricity

Question 27

What is the equation that links power, voltage and current?

Answer 27

P = V x I

Question 28

Why does a high current generate lots of heat?

Answer 28

Due to the resistance The resistance slows down the flow of electrons, and the energy lost in the process is released as heat

Question 29

Why is a high current bad when trying to transfer electricty?

Answer 29

Loses energy to thermal energy

Question 30

How do you make a circuit have a low current?

Answer 30

Increase the voltage

Question 31

What are step up transformers?

Answer 31

A device that increases the voltage in a circuit

Question 32

Why is a Step up transformer used in the National Grid?

Answer 32

It increases the voltage and decreases the current This is to minimise thermal energy energy loss to the surrounding This increases efficiency for Electrical power transmission

Question 33

What does ‘direct potential difference’ mean?

Answer 33

Potential difference in one direction only

Question 34

Why are Step Down transformers used in the National Grid?

Answer 34

It decreases the dangerously high voltage to a safer and more usable value (230V)

Question 35

Connecting the resistors in parallel would affect the total resistance of the circuit. Explain how.

Answer 35

It provides alternating pathways for the current This decreases the overall resistance of the current