Fields

Question 1

What is a force field?

Answer 1

a region in which a body experiences a non-contact force

Question 2

How is a force field represented?

Answer 2

as a vector

Question 3

How is a force field created?

Answer 3

interaction of mass/ static charge between moving charges

Question 4

What are the similarities between electrostatic and gravitational forces?

Answer 4

Both have inverse-square force laws that have
many characteristics in common,
eg use of field lines, use of potential concept, equipotential surfaces etc

Question 5

What are the differences between electrostatic and gravitational forces?

Answer 5

gravitational always attractive but electrostatic charges can repel

Question 6

What is gravity?

Answer 6

Universal attractive force acting between all matter

Question 7

How do you calculate the magnitude of the force between two point masses?

Answer 7

F = GMm/(r^2)

Newton’s law of gravitation

Question 8

What is G?

Answer 8

the gravitational constant, 5.57 x10^-11

Question 9

What is field strength?

Answer 9

the force applied by the field onto an object within the field

Question 10

How does mass affect the force of gravity?

Answer 10

the larger the mass, the larger the force of attraction

Question 11

What is a gravitational field line?

Answer 11

a line which indicates the direction of the gravitational force that would act on a test mass placed in the field

Question 12

What is a test mass?

Answer 12

a mass small enough not to affect the shape of the field with its own gravity

Question 13

What is the value of the Earth’s gravitational field strength, g

Answer 13

9.81

Question 14

How is gravitational potential energy calculated?

Answer 14

V = -GM/r

Question 15

Why is potential energy negative?

Answer 15

because work must be done to move towards infinity (against the force of attraction)

Question 16

What is work done in a gravitational field?

Answer 16

the GPE gained, W=mΔV

Question 17

What is a satellite?

Answer 17

something which orbits something else, eg moons, planets, stars etc

Question 18

Which way does an electric field travel?

Answer 18

positive to negative

Question 19

What is an electric field?

Answer 19

a region when a charged object will experience a force

Question 20

What is meant by charge?

Answer 20

1C of charge is transported by 1A of current in 1second

Question 21

What is static electricity?

Answer 21

a build up of electric charge on the surface of one object due to the removal or addition of electrons, usually caused by friction.

Question 22

What does it mean if field lines are closer together?

Answer 22

the field is stronger

Question 23

What is Coulomb’s law?

Answer 23

F = 1/4πε x QQ/r^2

Question 24

Are gravitational fields radial or uniform?

Answer 24

radial as they only noticeably occur in large masses (eg planets). the closer you get to the surface the more uniform they appear

Question 25

Are electric fields radial or uniform?

Answer 25

both

Question 26

How does the force experienced by a charge in a uniform electric field change?

Answer 26

it doesn't

Question 27

How is electric potential calculated?

Answer 27

``` V = E/Q v = 1/4πε x Q/R ```

Question 28

At which point from an electric field is there 0 potential energy?

Answer 28

infinity

Question 29

At which point from a gravitational field is there 0 potential energy?

Answer 29

infinity

Question 30

on a graph of gravitational field strength, g, against radius, r, what is given by the area under the graph?

Answer 30

Change in gravitational potential, ΔV

Question 31

What is Kepler's 3rd Law?

Answer 31

T^2 ∝ r^3

Question 32

Define escape velocity.

Answer 32

the lowest velocity which a body must have in order to escape the gravitational attraction of a particular planet or other object

Question 33

What is a geosynchronous orbit?

Answer 33

when an object is in a geosynchronous orbit around another, it appears to remain in a fixed point above one location on the surface. its orbit has the same time period as the planet in which it is orbiting, and so has a greater velocity as it must travel further (larger r from centre of earth than point on surface of earth)

Question 34

On a graph of E against r, what does the area under the curve represent?

Answer 34

ΔV