Section 9 - Gravitational and Electric Fields

Question 1

Is the force in a field contact or non-contanct?

Answer 1

Non-contact

Question 2

Is force a vector or scalar quantity?

Answer 2

Vector

Question 3

What are the similarities between electrostatic and gravitational forces?

Answer 3

• Inverse square force laws
• Potential concept
• Equipotential surfaces
• Use of field lines

Question 4

What are some differences between electrostatic and gravitational forces?

Answer 4

The gravitational forces from masses always attract, whilst charges may repel or attract

Question 5

What is gravity?

Answer 5

The universal attractive force which acts between all matter

Question 6

What is G?

Answer 6

The universal gravitational constant

Question 7

What can field lines tell you about a field?

Answer 7

The direction of the field and the strength of the field depending on the density of the field lines

Question 8

What is g?

Answer 8

• The force per unit area in a uniform field
• In a radial field the magnitude of g is the proportionality constant at that point between force and mass

Question 9

What is gravitational potential?

Answer 9

The work done/energy required in bringing 1 kg/unit mass from infinity to the point

Question 10

What is the work done by moving a mass in a field?

Answer 10

Mass x change in potential

Question 11

What is the gravitational potential difference?

Answer 11

Gravitational potential difference is the difference in the gravitational potentials of 2 points in a gravitational field

Question 12

What is an equipotential surface?

Answer 12

A surface in which every point on the surface has the same potential

Question 13

How much work is done when you move 1km in any direction on an equipotential?

Answer 13

No work is done when moving across equipotentials, as the potential at each point is the same

Question 14

Why is gravitational potential a negative value?

Answer 14

Work needs to be done to move an object from the inside of the field to the outside of the field
SInce outside the field’s potential is defined as 0 then the potential inside the field must be negative

Question 15

How is the orbital period related to the radius of a circular orbit?

Answer 15

T^2 ∝ R^3

Question 16

What equations could one use to find the speed of an orbiting satellite?

Answer 16

The orbiting object (mass m) is in circular motion, so we would use F = ma with F = GMm/r^2 rearranged to a=v^2 r=ω^2 x r.
This can be sold to find the speed (V0, angular speed (ω), the radius of the orbit or using T=2π/ω its period

Question 17

Compare the PE and KE of a lower orbit to a higher one

Answer 17

A lower orbit has less potential energy and more kinetic energy than a higher orbit

Question 18

What is the period of a geosynchronous orbit?

Answer 18

24 hours

Question 19

When calculating the force between two particles, what can air be treated as?

Answer 19

A vacuum

Question 20

For a charge sphere the charge can be assumed to be at what part of the sphere?

Answer 20

The centre

Question 21

Which is stronger? The gravitational force of subatomic particles or the electrostatic force

Answer 21

The electrostatic force

Question 22

Electric field line always go from ________ to ________.

Answer 22

Electric field lines go away from positive charge to negative charge

Question 23

What is electric field strength?

Answer 23

The force per unit charge acting at a point in an electric field

Question 24

What is the magnitude of E (electric field strength) in a uniform electric field?

Answer 24

Potential difference between plates (V)/ distance between plates

Question 25

What is the trajectory of a particle entering a uniform field at right angles?

Answer 25

It is parabolic

Question 26

How is electric potential related to electric field strength?

Answer 26

E = Δ V/Δ r
The change in electric potential with respect to the change in radius length

Question 27

What are the 2 relationships from Coulomb’s law?

Answer 27

E ∝ 1/r²
V ∝ 1/r

Question 28

What is the equation for escape velocity?

Answer 28

V = (2GM/r)^2