Fields and their consequences

Question 1

On a diagram what does the distance of the field lines represent?

Answer 1

Represents the strength of the force by the field

Question 2

How are Gravitational and Electric fields formed

Answer 2

Gravitational fields - interaction of masses
Electric fields - interaction of charges

Question 3

Similarities of electric and gravity fields

Answer 3

• both follow inverse square law
• both use field lines to be represented
• both have equipotential surfaces

Question 4

Gravity is always what?

Answer 4

Always attractive and acts on any object with a mass

Question 5

What does Newton’s law of gravitation show?

Answer 5

Shows that the magnitude of the gravitational force between two masses is directly proportional to the product of the masses.

Moreover the gravitational force is inversely proportional to the square distance between the centre of masses

Question 6

What are the two types of gravitational fields

Answer 6

Radial fields and uniform fields.

Question 7

What is the difference between radial fields and uniform fields?

Answer 7

Uniform fields the strength of gravitational force is the same throughout whilst in radial fields the force depends on the position of the object.

Question 8

How does gravitational field strength vary in different fields

Answer 8

Uniform fields - remains constant (g = f/m)

Radial fields - may vary (g = GM/r^2)

Question 9

What is Gravitational Potential

Answer 9

(V) is the work done per unit mass when moving an object from infinity to a point

Gravitational potential at infinity is zero, that is why gravitational potential (V) is always negative

Radial fields: V = -GM/r

Question 10

What is gravitational potential difference

Answer 10

The amount of energy needed to move a mass from two points

Work done = m * change in V

Question 11

What is known about equipotential surfaces? refer to work done

Answer 11

No work is done when moving along an equipotential surface as potential (V) is constant

Question 12

How can you workout gravitational field strength on a diagram

Answer 12

Find the gradient in a V-r graph

Question 13

When you plot (g) against (r) how do work out the gravitational potential difference

Answer 13

It is the area under the curve

Question 14

What is Keplers 3rd law

Answer 14

Square of an orbital period is directly proportional to the cube of the radius

T^2 = r^3

Question 15

How can you derive keplers third law

Answer 15

Centripetal force = gravitational force

Plug in V=2pi(r)/T

Question 16

How do you work out the total energy of a satellite

Answer 16

Kinetic energy + potential energy (this is constant)

e.g if height of satellite decreases, the potential energy decreases, however the kinetic energy increases at it will travel at a higher speed therefore total energy is kept constant

Question 17

What is escape velocity?

Answer 17

Escape velocity of an object is the minimum velocity it must travel at in order to escape the gravitational field at the surface of a mass

Kinetic energy = potential energy
1/2mv^2 = GMm/r

Question 18

What is a synchronous orbit

Answer 18

It is when the orbit of the satellite aligns with the orbit of the mass it is orbiting

Question 19

What are geostationary satellites

Answer 19

They orbit directly above the equator
Stay at the same point above earth
Used for TV and telephone signals

Question 20

What are low orbit satellites

Answer 20

Fast moving satellites with smaller orbital periods
- used to monitor the weather and military applications

Question 21

What is electric field strength

Answer 21

The force per unit charge experienced by an object in an electric field

E= F/Q

E = V/d (uniform field formed by parallel plates) (V is potential difference between plates)

E = Q/4(pi)(epsilon)(r^2) for radial fields

Question 22

What do electric field lines show

Answer 22

Shows the direction of a positive charge

Question 23

On an electric field graph against distance what does the area indicate

Answer 23

The electric potential of the sphere

Question 24

How does the radius of an ion differ when entering the same magnetic field at the same speed due to mass

Answer 24

As centripetal force acting on the ion is influence by mass, if they’re isotopes then their masses would differ hence their radius path would differ.

Question 25

State Newtons law of gravitation

Answer 25

The attractive force between two point masses
proportional to the product of the masses
inversely proportional to the square of the distance apart

Question 26

Explain why pendulum closer to a mountain would not point towards the centre of the earth

Answer 26

They’re gravitationally attracted to the centre of gravity of the mountain

Question 27

`describe two essential featured of the orbit needed for the satellite to appear geostationary

Answer 27

• equatorial orbit
• time period of 24 hours
• moves from west to east

Question 28

How does a satellite moving to a higher orbit affect the signal strength and contact time of the signal?

Answer 28

• signal would be weaker as the distance it travels is greater
• intensity decreases as distance increases
• signal is received for longer due to a wider beam width due to low angular speed

Question 29

Define escape velocity

Answer 29

Minimum speed needed for an object to escape a gravitational field