Gravitational Fields And Electric fields

Question 1

Describe Coulomb’s law of electric force

Answer 1

Coulomb’s Law states that the electrostatic force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them

Question 2

Define ‘electric field strength’

Answer 2

Electric field strength at a point is the force experienced per unit positive charge placed at that point in the field.

Question 3

Is field strength a scalar or vector?

Answer 3

Electric field strength is a vector quantity because it has both magnitude and direction

Question 4

Units of field strength?

Answer 4

Newtons per coulomb (N/C) or volts per meter (V/m).

Question 5

Define ‘electric potential’.

Answer 5

Electric potential (𝑉) at a point is the work done per unit positive charge to bring a test charge from infinity to that point.

Question 6

Is potential a scalar or vector?

Answer 6

Electric potential is a scalar quantity.

Question 7

Units of potential?

Answer 7

Volts (V)

Question 8

How do the field lines indicate field strength?

Answer 8

The closer the field lines, the stronger the electric field strength

Question 9

The angle between field lines and equipotentials?

Answer 9

Field lines and equipotential lines are always perpendicular to each other

Question 10

How can we use an E vs r graph to find the work done moving between points?

Answer 10

The work done moving between two points in the field is the area under the 𝐸 vs. 𝑟 graph between those points.

Question 11

How can we use a V vs r graph to find the field strength?

Answer 11

The electric field strength 𝐸 at a point is the negative gradient (slope) of the 𝑉 vs. 𝑟 graph
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Question 12

How can we use a V vs r graph to find the work done moving between points?

Answer 12

The work done moving a charge between two points is the difference in electric potential (Δ𝑉) multiplied by the charge 𝑄:
Workdone=Q⋅ΔV

Question 13

What is a force field?

Answer 13

A region in which a body experiences a non contact force

Question 14

How can forces be represented

Answer 14

Vectors

Question 15

What is newtons law of gravitation?

Answer 15

Non contact attractive Force between two masses is directly proportional to the product of the masses and inversely proportional to the distance between the centre of masses squared

Question 16

What is g?

Answer 16

Gravitational field strength, defined as the force per unit mass (vector quantity) it can also sometimes be referred to as the acceleration of a mass in a gravitational field.

Question 17

What is gravitational potential

Answer 17

The work done per unit mass to move a test mass from infinity to that point in the gravitational field

Question 18

How can there be a field strength of 0 at a point between sun and earth?

Answer 18

Because gravitational field strength (g) is a vector quantity thus there can be a point where g earth equals g sun

Question 19

Is gravitational potential vector or scalar?

Answer 19

Scalar

Question 20

Is gravitational field strength vector or scalar?

Answer 20

Vector

Question 21

Why is gravitational potential energy negative ?

Answer 21

Work is done on mass by gravity (negative work is done)

Question 22

What is the gravitational potential difference?

Answer 22

Work done per unit mass in moving a small test mass between two points in a gravitational field

Question 23

What are equipotential lines?

Answer 23

Lines that join points of equal gravitational potential so no work is done when moving along an equipotential (alway perpendicular to gravitational field lines)

Question 24

What is a satellite

Answer 24

A smaller mass orbiting a larger mass under the influence of gravitational force alone (remember speed is inversely proportional to orbital radius)

Question 25

How would you equate the T squared is directly proportional to r cubed/ root r cubed

Answer 25

Equate centripetal force and force due to gravity and put it in terms of V Then use T is equal to distance over speed substituting velocity found

Question 26

How will radius of a satellite affect speed?

Answer 26

T squared proportional to r cubed , so the greater the radius the slower it will travel and longer it will take to complete one orbit

Question 27

Describe kinetic and potential energy of a satellite

Answer 27

Always constant

Question 28

What is escape velocity?

Answer 28

Minimum speed an object must have at the surface of a planet or other body to escape it’s gravitational field without any further propulsion (work out by equating gravitational potential energy which is the potential times mass and then kinetic energy)

Question 29

What is a geostationary orbit?

Answer 29

When an orbiting object has an orbital period equal to the rotational period of the object it is orbiting (appear stationary relative to point on Earth) Orbital radius of around 42000km (36000km above earths surface) Orbital period of 24 hours

Question 30

What are low orbiting satellites?

Answer 30

Orbit between 180 and 2000km above earth they are cheap and less powerful but good for communication (orbital period is very fast about 90mins)