Turning points definitions

Question 1

Absolute motion

Answer 1

The (incorrect) idea that if an object is moving at a particular speed according to one observer, all other observers will observe the same thing.

Question 2

Absolute time

Answer 2

The (incorrect) idea that all observers, despite their relative motion, will measure the same time between events.

Question 3

Anode

Answer 3

Positive electrode or positive terminal.

Question 4

Black-body

Answer 4

A body that absorbs all the radiation incident upon it and reflects none. It is a perfect absorber and emitter of radiation – its temperature determines the total energy emitted at each wavelength.

Question 5

Cathode

Answer 5

Negative electrode, or terminal.

Question 6

Cathode ray

Answer 6

Rays emitted from the cathode in a discharge tube (which turned out to be a bean of electrons)

Question 7

Cathode ray tube

Answer 7

Apparatus in which an electron bean is produced (normally by thermionic emission), passes through a vacuum and hits a fluorescent screen.

Question 8

Corpuscular theory

Answer 8

Newton’s theory that light is made up of a stream particles, which he called corpuscles. He explained reflection and refraction by explaining what happened to components of the velocity parallel and perpendicular to the boundary.

Question 9

Discharge tube

Answer 9

A tube containing a low-pressure gas with a high voltage applied across it. Cathode rays (electrons) are emitted from the cathode.

Question 10

de Broglie hypothesis

Answer 10

That particles of matter such as electrons could have wave-like properties, with a wavelength given by λ = h/p, where h = Planck’s constant and p = momentum of the particle.

Question 11

Electromagnetic waves

Answer 11

A transverse wave in which the electric and magnetic fields oscillate perpendicular to each other, in phase with each other and perpendicular to the direction of propagation. Their speed in a vacuum is 3.00 x 108 ms-1

Question 12

Electron gun

Answer 12

A device in which electrons are produced by thermionic emission and accelerated through a potential difference to form a narrow beam of electrons.

Question 13

Fine beam tube

Answer 13

Apparatus used to determine the specific charge of an electron, consisting of an electron gun from which electrons are injected into a chamber containing a low pressure gas and a uniform magnetic field.

Question 14

Huygen’s wave theory

Answer 14

Light consisted of waves. To work out how the light will propagate, each point on a wavefront can be considered to be a source of secondary waves.

Question 15

Inertial frame of reference

Answer 15

a frame of reference that is not accelerating.

Question 16

Invariant

Answer 16

Independent of the motion of the source and the observer.

Question 17

Length contraction

Answer 17

The length of an object measured by an observer who is stationary relative to the object is longer than the length measured by an observer who is moving relative to the object.

Question 18

Null result

Answer 18

When the expected result of an experiment does not happen.

Question 19

Permeability of free space, μ0

Answer 19

A constant related to the magnetic flux density due to a current current-carrying wire in free space.

Question 20

Permittivity of free space, ε0

Answer 20

A constant related to the electric field strength due to a charged object in free space.

Question 21

Stokes’ law

Answer 21

The viscous drag force on a sphere moving through a fluid is given by F = 6πηrv, where η = viscosity of the fluid, r = radius of the sphere, v = velocity of the sphere.

Question 22

Thermionic emission

Answer 22

When a current passing through a filament causes the temperature of the filament to increase enough so that electrons in the filament gain enough kinetic energy to be released.

Question 23

Time dilation

Answer 23

The time between two events is shortest when measured by an observer who is stationary relative to the two events (for whom the events occur at the same coordinates in their frame of reference). Someone moving relative to the events will measure a longer time.

Question 24

Un-deflected

Answer 24

In this context, when a beam of charged particles (e.g. electrons) continues in a straight line because the magnetic force and electric force acting on each electron are equal and opposite.

Question 25

UV catastrophe

Answer 25

The incorrect prediction of wave theory that the intensity of radiation emitted from a blackbody should become infinite at smaller and smaller wavelengths. This would require an infinite amount of energy to emitted from the body.

Question 26

Viscosity

Answer 26

A measure of the resistance of a fluid to flow.