Section 7 - Fields

Question 1

Define an electric field

Answer 1

An area where a charge experiences a force

Question 2

Can non charged objects experience a force in an electric field?

Answer 2

No

Question 3

What are field lines?

Answer 3

Lines of force that show the direction of the force which act from positive to negative

Question 4

Define the diagram for a radial field with a positive charge in the centre

Answer 4

Positive charge in centre
Field lines with arrows act with arrows pointing away from the charge
Positive test charges repel

Question 5

Define the diagram for a uniform field for a positive and negative plate

Answer 5

Field lines are parallel and equally spaced
They go from positive to negative
Every point in the uniform field has the same force due to having the same density of field lines
Field lines end on a conductor at 90 deg

Question 6

Define electric field strength

Answer 6

Force per unit positive charge

Question 7

What is constant in a uniform field?

Answer 7

Electric field intensity

Question 8

Define breakdown field strength

Answer 8

The minimum field that causes an insulator to become electrically conductive

Question 9

Define electric potential

Answer 9

Work done per unit positive charge when moved from infinity (0V) to a given position on a positive test charge

Question 10

Define equipotentials

Answer 10

Lines or surfaces of constant potential

Question 11

State properties of equipotential lines

Answer 11

Movement along an equipotential surface requires no work, because such movement is always perpendicular to the electric field
Equipotential lines are perpendicular to field lines

Question 12

What happens to equipotential lines as field strength decreases?

Answer 12

They get further apart

Question 13

Define Coulomb’s law

Answer 13

Any 2 point charges exert a force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between then

Question 14

What type of particles can be accelerated by an electric field?

Answer 14

Charged particles

Question 15

Work done by an electric field =…

Answer 15

Change in Ek

Question 16

Define capactiance

Answer 16

Charge stored per unit voltage

Question 17

What is RC

Answer 17

Time constant - time it takes the voltage to drop by 1/e

Question 18

Describe how to draw a graph for the discharge of a capacitor

Answer 18

Voltage/V y against time/s x
Curve looks like a reciprocal graph
Curve starts touching y axis at Vo 
Initial gradient can't be vertical
Curve must not touch x axis

Question 19

What does capacitance depend on?

Answer 19

Geometry of capacitor

Question 20

What are dielectrics?

Answer 20

Insulators in capacitors

Question 21

What does adding an insulator (dielectric) do to capacitance?

Answer 21

Increases capacitance as it allows more charge to be stored per unit voltage

Question 22

What 3 things does a dielectric do

Answer 22

• Keeps plates separated
• Incresaes maximum working voltage
• Increases capacitance by a factor of Er (relative permittivity)