10 Energy and Voltage- 4th Form

Question 1

Why would an appliance NOT need an Earth wire?

Answer 1

It is double insulated

It has a plastic casing OR the electrical components are incased by plastic

Question 2

Define voltage

Answer 2

Energy per unit charge either supplied by a cell, or transferred to a component.

Question 3

What type of current is shown in the image?

Answer 3

Alternating current

Current that constantly changes direction

i.e. 50 Hz or 50 times a second

Question 4

What is voltage measured in?

Answer 4

Volts or V

Question 5

What is the voltage across a cell or power supply a measure of?

Answer 5

The energy transferred from chemical store electrically to the wires per coulomb

Question 6

What component symbol is shown below?

Answer 6

ammeter

Question 7

Define current

Answer 7

• The rate of flow of charge

OR

• the number of coulombs passing a point in a circuit per unit time

(It is not the speed of the electrons!)

Question 8

Which wire is circled in the image?

Answer 8

Earth wire

Question 9

The IV graph below shows a line for fixed resistor. How would the line change for a resistor with half the resistance?

Answer 9

It would be steeper

It would have double the gradient

It would have double the current for the same volts

Question 10

What is the effect of current in a resistive wire?

Answer 10

Moving electrons in the wire collide with the metal ions

They transfer energy electrically to the wire

The wire heats up -gains a thermal store

When hot enough the wire may glow - radiate energy

Question 11

How will the current change if the resistance of a circuit is decreased for the same voltage?

Answer 11

current will increase

Question 12

How does a fuse work?

Answer 12

• If the current exceed the fuse rating (surge in current)
• the fuse wire heats up and melts
• This breaks the circuit and isolate the appliance
• protecting it from overheating/fire

Question 13

To investigate how the currect varies with voltage in a filament bulb, fixed resistor and diode you should use the cirucit below.

Why does the circuit need a variable resistor?

Answer 13

To vary the voltage across the component

Independent variable is voltage

Dependent variable is current

Question 14

The plastic around wires keep us safe. Explain

Answer 14

Plastic is an insulator.

No current can flow through an insulator

no risk of electric shock

Question 15

What is resistance?

Answer 15

• The tendency of a material to resist the flow of an electrical current.
• A measure of how much voltage is needed per amp of current.

Question 16

Below is an IV graph for a…..

Answer 16

diode

Question 17

How is voltage related to energy and charge?

Answer 17

V=E/Q

Voltage = Energy / Coulomb

Voltage lost across a component is a measure of the energy lost across the component per coulomb

Question 18

What is power measure in?

Answer 18

Watts (W)

Question 19

How does an Earth wire and a fuse work together to protect the user of an appliance

Answer 19

• The Earth wire is connected to the metal casing of the appliance
• if the live wire works loose (fault) and touches the metal casing
• there is a surge in current through to the Earth wire
• this melts the fuse wire
• isolating the appliance
• preventing an electric shock

Question 20

What is a watt?

Answer 20

1 W = 1 J/s

I Watt = 1 joule per second

Question 21

What is a volt?

Answer 21

1 V = 1 J/C

1 volt = 1 joule per coulomb

Question 22

How does voltage related to current and resistance?

Answer 22

V=IR

Question 23

What are the prongs of a plug made of brass but the wires made of copper?

Answer 23

Brass is strong and will not bend

Copper is a good conductor of electricity and ductile (can be drawn into wires)

Question 24

Below is the symbol for…

Answer 24

a double insulated appliance

Question 25

What is the Earth wire connected to in the appliance

Answer 25

The metal casing

Question 26

What is the unit for current?

Answer 26

ampere / amps or A

Question 27

What component symbol is shown below?

Answer 27

voltmeter

Question 28

What is the unit for energy?

Answer 28

joules (J)

Question 29

How is power related to current and voltage?

Answer 29

P=IV

Question 30

What component symbol is shown below?

Answer 30

Fuse

Question 31

How is energy related to current, voltage and time?

Answer 31

E = IVt

Question 32

A fuse protects the appliance and the user….explain

Answer 32

• the fuse will blow if there is a surge in current to the appliance. This protects the appliance from overheating (being damaged)
• the fuse will blow if a fault occurs in the appliance. The surge of current down the Earth wire blows the fuse and prevents an electric shock

Question 33

Name the parts of a plug

Answer 33

1. Cable grip

2 Neutral wire

3. Earth wire
4. Live wire
5. Fuse

Question 34

What is the difference between d.c. and a.c. current/voltage

Answer 34

Direct current - current flows in one direction only (i.e. cell)

Alternating current - current continuously changes direction (i.e. mains supply)

Question 35

Describe what it means when 1 A is passing through a circuit

Answer 35

1 A = 1 Coulomb per second

Question 36

The IV graph below is for an ohmic conductor…

Give an example of an ohmic conductor.

Answer 36

1. fixed resistor
2. wire (if at constant temperature)

Question 37

Below is the IV graph for a….

Answer 37

filament bulb

Question 38

What component symbol is shown below?

Answer 38

variable resistor

Question 39

What component symbols are shown below?

Answer 39

battery/two cells

&

solar cell

Question 40

What would happen if a plug is wired incorrectly and the live wire is attached to the Earth prong

Answer 40

The Earth prong is wired to the metal casing of the appliance

The metal casing of the appliance will be live with 240V wired to it.

Risk of electric shock to user