Gravitational and Electric Fields

Question 1

Force Field?

Answer 1

A region in which a body experiences a non-contact force. They arise from interactions between objects and only objects with large masses like stars produce fields of significant effect

Question 2

Radial Field Lines properties?

Answer 2

Show the direction of force objects would experience in the field. They are attractive so go towards the larger mass and will all meet at the centre. Field strength and force experience decrease with distance. Higher density of field lines show a stronger gravitational field

Question 3

Point Mass?

Answer 3

A mass with a negligible volume or a uniform sphere that acts as if it is concentrated towards its centre. Point masses have radial gravitational fields

Question 4

Law of Gravitation?

Answer 4

This is an inverse square where F ∝ 1 / r^2 where “r” is the distance between two masses centre of mass

Question 5

Gravitational Field Strength?

Answer 5

The force per unit mass and depends on the position of the object in the field

Question 6

“g” against “r” graph?

Answer 6

A reciprocal curve that at smaller values of “r” has the greater value of “g” for that particular field. The area under the curve can be used to identify the gravitational potential

Question 7

Gravitational Potential?

Answer 7

The gravitational potential at a point is the gravitational potential energy a unit mass would have at that particular point. It is negative of the surface of a mass and gets less negative with an increasing distance and at infinity is zero

Question 8

“V” against “r” graph?

Answer 8

The gradient at a particular point on the curve is the gravitational field strength at that point

Question 9

Gravitational potential difference?

Answer 9

The energy needed to move a unit mass. Different points will have different gravitational potentials so there is a potential difference between two points and this is the energy to move the object this distance

Question 10

Gravitational Potential Energy Formula?

Answer 10

Ep = GMm / r

Question 11

Equipotentials?

Answer 11

Lines in 2d or surfaces in 3d that join the points together that all have the same gravitational potential. Equipotentials and field lines are always perpendicular. No work is done moving along an equipotential and an electrical charge can travel along one without energy being transferred

Question 12

Satellite?

Answer 12

Any smaller mass which orbits a much larger mass and are kept in orbit by gravitational forces which in satellites in circular orbits provide the necessary centripetal force

Question 13

Orbital Period?

Answer 13

The time it takes for a satellite to complete one orbit. The greater the radius of orbit the slower it travels in the orbit so its orbital period would increase

Question 14

Orbital Speed Proof?

Answer 14

Centripetal Force:
F = mv^2 / r
Gravitational Force:
F = GMm/r^2
Making Forces equal:
v = √GM/r
Time equation:
T = 2πr / v
T = 2πr / √GM/r
T = √4π^2r^3 / GM

Question 15

KE and potential energy in orbits?

Answer 15

In a circular orbit the speed and distance to the mass are constant meaning its potential energy and KE is constant. In an elliptical, squashed circle, orbit the speed increases as radius decreases meaning its KE increases and potential energy decreases but the total is constant

Question 16

Escape Veloctiy?

Answer 16

The minimum speed an unpowered object needs in order to leave a gravitational field and not return towards the larger mass from its attractive gravitational force. The equation is: v = √2GM/r

Question 17

Geostationary Satelites?

Answer 17

Have a synchronous orbit meaning the orbital period is the same as the rotational period. In the same point above Earth and have to be on the equator so its angular speed is constant which is needed to allow it in the same position

Question 18

Uses of Satelites?

Answer 18

Geostationary satellites are useful for communications and since their position doesn’t change the angle of the receiver doesn’t have to change. Low orbit satellites are used in communications and are cheaper but need several to work together to maintain constant coverage. Imaging satellites are used for things like monitoring the weather

Question 19

Gravitational Fields compared to Electric Fields?

Answer 19

Electric fields can either be attractive or repulsive whereas gravitational fields are always attractive

Question 20

Electric Fields?

Answer 20

The region in which any charge can either attract or repel other charges. If a charged object is placed in an electric field it will experience a force

Question 21

Coulombs Law?

Answer 21

Identifies the force of attraction or repulsion between 2 point charges in a vacuum. It has the equation: F = 1/4πε0 x Q1Q2/r^2. The force on Q1 is always equal and opposite to the force on Q2. It is also an inverse square law so the further the charges are apart the weaker the force between them

Question 22

Electric Field Strength?

Answer 22

The force per unit of positive charge and is the force a charge of +1 C would experience in an electric field

Question 23

Electric Field Lines?

Answer 23

Drawn to show the direction of the force on a positive charge. For parallel plates the field lines point from the plate with the positive voltage to the plate with the less positive voltage

Question 24

Non-Point charges electric field strength?

Answer 24

A point charge or a sphere with charge evenly distributed across its surface have an inverse square relationship with electric field strength and the distance from the charge. Objects that aren’t point charges don’t have this relationship

Question 25

Parallel plates properties?

Answer 25

In E = V / d the value of "V" is the difference in potential difference between the parallel plates. Connecting two parallel plates to opposite poles of a battery produces a uniform field.

Question 26

Absolute Electric Potential?

Answer 26

This is the electric potential energy that a unit positive charge of +1C would have at a particular point. It depends on how far the point is from the charge creating the electric field and the size of the charge. It's greatest on the surface of the charge and decreases as distance from the charge increases. Its equation is: V = 1/4πε0 x Q/r

Question 27

Electric Potential Difference?

Answer 27

If two points in an electric field have a different absolute electric potential then it means they have an electric potential difference. This is the energy needed to move a unit charge between those points. This is the area between two "r" values on a "E" against "r" graph

Question 28

Energy and moving charges?

Answer 28

To move a charge across a potential difference energy is needed. The amount of energy otherwise work depends on the size of the charge and the size of the potential difference its moved across