Electricity

Question 1

What is a vacuum?

Answer 1

No matter in a volume of space
Like charges repel
Unlike charges attract
Attraction is effected by distance

Question 2

Charges flow in materials

Answer 2

When charges move, they produce a magnetic field, moving anticlockwise

Question 3

Like charges

Answer 3

Repel, force is positive

Question 4

Unlike charges

Answer 4

Attract, force is negative

Question 5

What is the force equation?

Answer 5

Product of the charges divided by the distance squared

Question 6

What is the SI unit for charge?

Answer 6

Coulomb

Question 7

Explain a focusing cap on an X-ray tube

Answer 7

To keep the electrons focused on the target anode, and thus creating a sharper image. Keeping the flow of electrons repelling and confined in the area of movement towards the target.

Question 8

Define electrical potential

Answer 8

Work done in moving a unit charge from infinity to that point

Question 9

What is the SI unit for electrical potential

Answer 9

Volt

Question 10

Define potential difference

Answer 10

The difference in work done moving a unit charge from one point to another

Question 11

What is electromagnetic force (EMF)

Answer 11

The driving force across a power source (negative charge flows from a negative to positive potential)

Question 12

Conduction band

Answer 12

Free electrons

Question 13

Forbidden zones

Answer 13

Electrons cannot travel freely

Question 14

Valence band

Answer 14

Electrons can freely move from the outer shell

Question 15

Filled band

Answer 15

Complete shells

Question 16

Insulators

Answer 16

Require more energy for electrons to enter conduction band as the forbidden zone is larger
Must increase temperature and Voltage

Question 17

Semi-conductors

Answer 17

Requires less energy as the forbidden zone is shorter
At an increased temperature, more electrons will enter the conduction band, but at room temperature some will enter anyway

Question 18

Conductors

Answer 18

No forbidden zone, so electrons can freely pass through bands (random movement)

Question 19

What happens as charge storage increases?

Answer 19

Repulsive effect slows down storage
To increase, increase the size of the storage capacitator, or the potential difference

Question 20

What is capacitance?

Answer 20

The quantity of charge which can be stored on a conductor per unit potential

Question 21

What is the SI unit for capacitance?

Answer 21

Farad

Question 22

What is a capacitor?

Answer 22

A device used to store electrical current, consists of two electrode conductors and a separating insulator

Question 23

What does the insulating layer do in a capacitor?

Answer 23

Prevents contact between the two plates, thus preventing charge flow
Increases the capacitance of the capacitor

Question 24

What effects capacitance?

Answer 24

Distance between plates
Area of plates

Question 25

Uses of capacitors

Answer 25

Voltage smoothing (overcomes X-ray energy fluctuations) Timing circuits (signal sent to end exposure when capacitor reaches max)

Question 26

State some facts about electron flow

Answer 26

Direction of movement is equally random Resistance to flow is affected by temperature due to increased collisions

Question 27

What is electrical current?

Answer 27

Flow from negative to positive

Question 28

What is convectional current?

Answer 28

Flow from positive to negative

Question 29

What is the SI unit for current?

Answer 29

Ampere

Question 30

How do you work out the electric charge flowing through an X-ray tube during an exposer?

Answer 30

milliamps x time(s)

Question 31

What is the SI unit for resistance and what is resistance?

Answer 31

Ohms Collisions between vibrating electrons

Question 32

What factors affect resistance?

Answer 32

Length Cross sectional area Conductor or insulator? Temperature

Question 33

What is Ohm's Law?

Answer 33

The current flowing through a conductor is directly proportional to the potential difference between its ends

Question 34

What is the equation for Potential Difference?

Answer 34

V + I x R (V=potential difference I= current R= resistance)

Question 35

What is electrical power?

Answer 35

The rate of doing work Power= voltage x current

Question 36

How do you minimise power loss?

Answer 36

High voltage and low current

Question 37

How to reduce resistance?

Answer 37

Copper Increase cross sectional area

Question 38

Electrical safety features

Answer 38

Isolation Insulation Earthing Restricted access