Unit 4

Question 0

What is gravitational field strength?

Answer 0

The force per unit mass at that point.

Question 1

What is Newton’s Law of Gravitation

Answer 1

Two particles attract each other with a force that is proportional to the product of their masses and inversely proportional to the square of their separation.

Question 2

What is gravitational potential?

Answer 2

The work done in moving a unit mass to that point from infinity, where the potential is defined as zero

Question 3

What is the relationship between gravitational field strength and gravitational potential?

Answer 3

The gravitational field strength is equal to the magnitude of the gradient of the graph of gravitational potential against radius, at any given radii.

Question 4

What are the characteristics of a geostationary orbit?

Answer 4

Period = 1 day Orbiting above the equator. Same direction as the earth

Question 5

What are the conditions for escape? (Reaching the escape velocity)

Answer 5

The kinetic energy must raise the gravitational potential to zero.

Question 6

What path does a particle in a uniform gravitational field take?

Answer 6

Parabolic

Question 7

What is Coulomb’s Law

Answer 7

The force between two charges is directly proportional to the product of their charges and inversely proportional to the square of their separation.

Question 8

What is Electric Field Strength?

Answer 8

The force per unit positive charge at that point.

Question 9

What path does a charged particle in a uniform electric field take?

Answer 9

Parabolic

Question 10

What is ‘electric potential’?

Answer 10

The work done in moving a unit positive charge to that point from infinity, where the potential is defined as zero.

Question 11

What is the relationship between ‘electric field strength’ and ‘electric potential’?

Answer 11

The ‘electric field strength’ is the gradient of the graph of ‘electric potential’ against ‘radius’.

Question 12

What is capacitance?

Answer 12

The capacitance of a capacitor is a measure of its ability to store charge. See formula.

Question 13

What happens to the charge, current and potential difference across a capacitor as it discharges.

Answer 13

They undergo exponential decay. See formula.

Question 14

How do p.d. and charge vary with time whilst charging a capacitor?

Answer 14

The increase following a ln curve starting at the origin.

Question 15

How does current vary when a capacitor is charging with time?

Answer 15

It decreases following an exponential decay.

Question 16

Explain the distribution of p.d. during charging if a capacitor through a resistor.

Answer 16

At first no charge on capacitor so no p.d. All the supply p.d. across the resistor. As charge builds up on the capacitor the p.d. across it rises and the p.d. across the resistor falls. When fully charged the p.d. across the capacitor reaches that of the supply voltage and the p.d. across the resistor is zero.

Question 17

What is ‘magnetic field strength’/’magnetic flux density’?

Answer 17

The magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines. Measured in Teslas.

Question 18

What is a ‘line of force’ of a magnetic field?

Answer 18

A line at which a ‘free’ North Pole would move in the field.

Question 19

What is Faraday’s Law?

Answer 19

As a magnet moves through a coil the induced emf increases if: •The magnet is moved faster. •The magnet is stronger •There are more turns on the coil •The cross sectional area if the coil is increased

Question 20

What path do charged particles in a magnetic field follow and why?

Answer 20

The path is circular because the force is always at right angles to the motion.

Question 21

What is ‘magnetic flux’?

Answer 21

The magnetic flux is a measure of the number of magnetic field lines passing through a region.

Question 22

What is ‘Lenz’s Law’?

Answer 22

The induced emf will be such that it would produce a current in the coil which will oppose the change producing it.

Question 23

How do you calculate induced emf?

Answer 23

The product of the magnetic field strength and the area swept out per second.

Question 25

What are the energy losses in a transformer?

Answer 25

Eddy currents - induced emfs in the metal block Ohmic heating of coils Flux fails to pass through secondary coils Hysteresis losses - overcoming internal friction when the dipole reverses

Question 26

What is the area under a force-time graph?

Answer 26

Change in Momentum/Impulse

Question 27

What is the ‘Principle of conservation of Momentum’?

Answer 27

When two or more bodies act upon one another, their total momentum remains constant, provided that no external forces act.

Question 28

What is the difference between elastic and inelastic collisions?

Answer 28

An elastic collision is one where no energy is lost, whereas an inelastic collision results in loss of energy.

Question 29

What are the conditions for SHM?

Answer 29

A body undergoes simple harmonic motion if its acceleration is always directed towards a fixed point and is directly proportional to its distance from that point.

Question 30

What graphs represent displacement, velocity and acceleration in SHM?

Answer 30

Displacement = cosx Velocity = -sinx Acceleration = -cosx

Question 31

In SHM, where is acceleration maximum?

Answer 31

At the extremes of displacement. When x=A.

Question 32

In SHM, where is velocity maximum?

Answer 32

When the object passes through the equilibrium point.