Main definitions

Question 1

a Torque

Answer 1

when a force causes a rotation around an axis

increase in radius->increase in torque->easier to open door

Question 2

Moment of inertia

Answer 2

the measure of an object’s resistance to angular acceleration around a given axis

Question 3

moment of inertia equations:
point mass
rod about centre
rod about end
disc about centre
sphere about centre

Answer 3

point mass-hoop or hollow cylinder

rod about centre-horizontal rod with vertical axis down its middle

rod about end-end of horizontal rod touching vertical axis at right angle

disc about centre-solid cylinder or disc

sphere about centre-sphere

Question 4

The principle of conservation of angular momentum

Answer 4

In the absence of external torques, total angular momentum before equals the total angular momentum after

I1wo1+I2wo2=I1w1+I2w2

Question 5

Gravitational field strength

Answer 5

defined as the gravitational force acting on a unit mass by a gravitational field

Question 6

Conservative field

Answer 6

A field in which the work done (energy required) to move mass between two points in the field is independent of the path taken

e.g. gravitational field

Question 7

gravitational potential (at a point in a field)

Answer 7

The work done (energy) in moving 1kg of mass from infinity to that point in the field.

Question 8

Escape velocity

Answer 8

the minimum velocity needed for a mads to escape the gravitational field of an object completely (ie to reach infinity)

Question 9

The equivalence principle

Answer 9

It is not possible to distinguish between the effects on an observer of a uniform gravitational field and of a constant acceleration

Question 10

A geodesic

Answer 10

the shortest distance between two points

Freely moving objects and light (due to gravitational lensing) will follow geodesics in spacetime

Question 11

Schwarzschild radius

Answer 11

radius/distance from the singularity (up to the event horizon) where spacetime is so distorted that not even light can escape it

(its escape velocity exceeds the speed of light)

Distance from the centre of a black hole to the event horizon

Question 12

What interpretation does general relativity lead to?

Answer 12

that mass curves spacetime and that gravity arises from the curvature of spacetime

Question 13

Luminosity of a star

Answer 13

the energy per second (power) a star radiated across all wavelengths into space

Question 14

Apparent brightness

Answer 14

the luminosity falling on 1m^2 at a distance d from the star

Question 15

Quantum physics

Answer 15

‘phenomena on the atomic scale which are observed to be quantised - i.e. only exist in well defined states rather than a continuous range’

Question 16

Heisenberg’s uncertainty principle

Answer 16

It is not possible to know the position and momentum of a quantum particle simultaneously

It is not possible to know the lifetime and the associated energy change of a quantum particle simultaneously

Question 17

Quantum tunneling

Answer 17

Potential wells form energy barriers which would not normally allow particles to escape.

The quantum particle can ‘borrow’ energy for a short period of time and occupy states that, according to classical physics, it has insufficient energy to occupy

Question 18

Explanation if helical motion

Answer 18

Charged particles entering a magnetic field at an angle will travel in a helical path due to the combination of its circular motion perpendicular to the field and its linear motion parallel tot he field

Question 19

simple harmonic motion

Answer 19

The restoring force (and acceleration) is directly proportional to, and in the opposite direction to, the displacement from the rest position

Question 20

What does damping refer to?

Answer 20

The energy lost from an oscillating system over time. The result is that amplitude of the oscillation decays over time (underdamping

Question 21

overdamping and critical damping

Answer 21

-the object is brought slowly back to equilibrium with no oscillations

-the oscillator comes to a stop in the minimum possible time e.g. car shock absorbers

Question 22

wave

Answer 22

A disturbance in a medium which transfers energy from one place to another

Question 23

Amplitude

Answer 23

A measure of the energy transferred by a wave- as amplitude increases, so does energy transferred

Question 24

What is the phase difference between 2 points on a wave a distance x apart?

Answer 24

Their separation as a fraction of the wavelength, expressed as a phase angle in radians

Question 25

When is a stationary wave formed?

Answer 25

**When the incident wave and the reflected wave interfere to produce points if destructive and constructive interference** **The waves reflected from each end interfere to produce maxima and minima** By the interference between 2 waves of the same frequency and amplitude, travelling in different directions

Question 26

Transverse waves

Answer 26

oscillations of the wave medium are at right angles to the direction if travel

Question 27

unpolarised transverse waves

Answer 27

They can have oscillations in any random direction, just as long as they are at right angles to the direction of travel

Question 28

Plane polarised light

Answer 28

**The oscillations of the wave are restricted to 1 plane** It has oscillations of the electric field vector restricted to a single plane

Question 29

non-inertial frames of reference

Answer 29

frames of reference that are accelerating with respect to an inertial frame

Question 30

electric field strength

Answer 30

the force exerted on a unit charge by an electric field

Question 31

Electrical potential

Answer 31

The electrical potential at a point in an electric field is ‘the work done in moving a unit charge from infinity to that point in the field’ (0 at infinity) (can be + or -)

Question 32

Conservative field (electromagnetism)

Answer 32

The energy (work done) in moving a charge between any 2 points in a field is independent of the path taken between the points

Question 33

Capacitive reactance

Answer 33

A capacitors opposition to the flow of a.c current (ohms)