Electricity

Question 1

What is needed for electrical charge to flow through a closed curcuit?

Answer 1

A source of potential difference

Question 2

What is electric current?

Answer 2

A flow of electrical charge

Question 3

What is the size of electric current?

Answer 3

The rate of flow of electrical charge

Question 4

What is charge flow measured in?

Answer 4

Coulombs

Question 5

What is current measured in?

Answer 5

Amperes

Question 6

What does the current through a component depend on?

Answer 6

The resistance and potential difference of the component

Question 7

How are resistance and current linked?

Answer 7

The greater the resistance of the component, the smaller the current for a given potential difference

Question 8

What is potential difference measured in?

Answer 8

Volts

Question 9

What is resistance measured in?

Answer 9

Ohms

Question 10

What happens when the temperature of a filament increases?

Answer 10

• resistance increases

Question 11

What happens when the temperature of a thermistor increases?

Answer 11

• resistance decreases

Question 12

What are some applications of thermistors?

Answer 12

• thermostats
• car engine temperature sendors

Question 13

What happens when light intensity on an LDR increases?

Answer 13

• resistance decreases

Question 14

What are the applications of LDR’s?

Answer 14

• automatic night lights
• outdoor lighting
• burgular lighting

Question 15

What are components connected in series like?

Answer 15

• same current through each component
• total potential difference of power supply shared between the components
• total resistance of two components is the sum of resistance of each component

Question 16

what is the equation for total resistance?

Answer 16

resistance 1 + resistance 2 (ohms)

Question 17

What is the mains current in UK?

Answer 17

230V

Question 18

What is the mains frequency UK?

Answer 18

• 50Hz

Question 19

Describe the live wire.

Answer 19

• Brown
• carries alternating potential difference from the supply

Question 20

Describe the neutral wire.

Answer 20

• Blue
• at or close to, earth potential (0V)
• completes the curcuit

Question 21

Describe the earth wire.

Answer 21

• Green and yellow stripes
• 0V, only carries current if there’s a fault

Question 22

What is power measured in?

Answer 22

Whatts

Question 23

Why is the live wire dangerous?

Answer 23

• causes large electrical shock that could injure or even kill you
• could result in fires in contact with earth wire

Question 24

What is the national grid?

Answer 24

• system of cables and transformers linking power stations to consumers

Question 25

What do step up tranformers do?

Answer 25

- increase PD from power station to transmission cables - decrease current - to reduce energy loss

Question 26

What do step down transformers do?

Answer 26

- decrease potention difference - increase current - for domestic use

Question 27

Describe static electricity.

Answer 27

- insulating materials rubbed against each other and become electrically charged - negatively charged electrons rubbed off one material and on to other - material that gains electrons become negatively charged - material that loses electrons becomes positively charged

Question 28

Describe what happens when two electrically charged objects are brought together.

Answer 28

- exert a force on each other - repel if carry same charge - attract if carry opposite charges - attraction and repulsion non contact forces

Question 29

Describe electric fields.

Answer 29

- charged object creates electric field around itself - field strongest close to charged object - further away from the charged object, weaker field

Question 30

how do the earth wire and fuse protect user from electric shock?

Answer 30

• fault develops when live wire touch metal casing • resistance in live wire reduces • current in live wire increases • earth wire takes current from live wire • at the same time fuse melts • so no more current flows into live wire

Question 31

how do the earth wire and fuse protect user from electric shock?

Answer 31

• fault develops when live wire touch metal casing • resistance in live wire reduces • current in live wire increases • earth wire takes current from live wire • at the same time fuse melts • so no more current flows into live wire