Define: conservation of momentum

In any collision or explosion, total momentum remains constant provided no external forces act.

Define: elastic collision

No kinetic energy is lost

How are force and momentum related?

Force = rate of change of momentum

What is meant by 'impulse'?

The product of force and time

Define the term 'radian'

1 radian is the angle subtended by a circle of radius r by an arc of length r

Define: angular speed

The angle in radians turned through in 1s

Give 3 factors that affect centripetal force

mass
speed
radius (of circle)

What conditions must be satisfied for an object to be in SHM?

1. The acceleration of the object is proportional to its displacement from the equilibrium position.
2. The acceleration is always directed back towards the equilibrium position.

Energy in SHM is the interchange between which two energy forms

Kinetic and potential

How is the oscillations of a simple pendulum and a massspring system affected if taken to the Moon?

simple pendulum  longer time period
massspring  no effect

What is a free vibration?

System displaced and left to oscillate at its natural frequency

What is a forced vibration?

System driven at frequency other than natural frequency

What happens when a system is driven at its natural frequency?

Resonance
Amplitude of oscillations increases

What is damping?

Resistive force that causes amplitude of oscillations to decrease

What is critical damping?

System returns to equilibrium as quickly as possible without 'overshooting'

State Newton's gravitational law

Gravity is an attractive force between point masses that is proportional to the product of the two masses and inversely proportional to the square of the distance between them

What do gravitational field lines show?

The direction a small test mass would move when placed in the gravitational field

Describe in one word the gravitational field around a planet

Radial (inwards)

What is an equipotential?

A region / surface of constant potential

Define: gravitational field strength

The force per unit mass acting on a small test mass placed in a gravitational field

Define: gravitational potential

The energy required to bring a unit mass from infinity to some point in a gravitational field, this is work done by gravity

Why is gravitational potential a negative value?

Work is done to reach infinity at which point gravitational potential is zero

What is the gradient of a gravitational potential vs. distance graph equal to?

Gravitational field strength

Define: electric field strength

The force per unit charge acting on a small positive charge at that point

What is the unit for electric field strength?

Newton per Coulomb or Volt per metre

What is the unit for gravitational field strength?

N / kg

Define: electric potential

The work done in bringing a unit positive charge from infinity to that point

How do you find the electric potential difference between two points in an electric field?

The work done in moving a unit positive charge from the point at the lower potential to that at the higher potential

What is the unit for electric potential difference?

Volt, V

What is the electric field strength equal to in a uniform field?

E = V / d

What is the force F on a charge q equal to in an electric field of field strength E?

F = qE = qV / d

Describe the motion of a charged particle entering a uniform electric field perpendicular to the field lines

parabolic

Give one difference between electric and gravitational fields

Act on charges instead of masses
or
Can be attractive or repulsive, g fields are only attractive

Define capacitance

charge stored / potential difference

Define the Farad, F

1 Coulomb stored when a p.d. of 1 Volt is applied

What does the area under of a graph of Q against V represent?

Energy stored

What does the gradient of a graph of Q against V represent?

Capacitance

What is the time constant of a capacitor equal to?

RC

After how many time constants is a capacitor considered to be charged or discharged?

5

Define: magnetic flux density

Force per unit current per unit length

Fleming's left hand rule:
State what the 3 fingers represent

First finger: B field
Second finger: Current
Thumb: Force

Fleming's right hand rule:
State what the 3 fingers represent

First finger: B field
Second finger: Current
Thumb: Force

Why does a particle moving in a circular path not spiral inwards?

Force is perpendicular to the velocity at any time
The force causes a change in direction, but not a change in the magnitude of the velocity
No work is done in the direction of the force

State Lenz's law

The direction of the induced EMF is such that the current it causes to flow opposes the change which causes it

Define: magnetic flux and state the unit

Product of B and A
Webers, Wb

Define: magnetic flux linkage and state the unit

Product of the number of turns on a coil and the magnetic flux (NBA)
Unit: Weberturns

How is the induced EMF and the flux linkage related?

Rate of change of flux linkage = magnitude of induced EMF

Describe how a p.d. is induced across the secondary coil of a transformer

An alternating p.d. across the primary coil produces an alternating magnetic field in the iron core.
This is linked to the secondary coil.
An alternating p.d. is induced across the secondary coil.

Describe how the efficiency of a transformer is maximised.

The core is made from iron which can be magnetised and demagnetised quickly.
The core is laminated, reducing eddy currents.
Low resistance wire is used for the coils, reducing the heating effect of the current.

Why is electricity transmitted at high potential differences?

High p.d. means low current.
Low current means less energy transferred to the surroundings, increasing efficiency
