Module 4 defintions

Electric current

Rate of flow of charge

Conventional current

Current from a positive to negative terminal (opposite to electron flow)

Conservation of charge

Electrical charge cannot be created or destroyed

Kirchhoff’s first law

for any point in an electrical circuit, the sum of the currents into that point is equal to the sum of the currents out of that point

Mean drift velocity

The average velocity of electrons as they move through a wire

Number density

The number of free electrons per cubic metre of material

Potential difference

The energy transferred from electrical energy to other forms per unit charge

1 volt

The p.d. across a component when 1J of energy is transferred per unit charge passing through the component

E.m.f.

The energy transferred from chemical energy to electrical energy per unit charge

Resistance

How difficult it is for current to flow through a material

Unit ohm

The resistance of a component that has a potential difference of 1V per unit ampere

Kilowatt-hour (kWh)

The energy transferred by a device with a power 1000W of operating for a time of 1hr (3.6MJ)

Potentiometer

Variable resistor with three terminals and a sliding contact

Kirchhoff’s second law

In a closed loop of an electrical circuit, the sum of the e.m.f.s is equal to the sum of the p.d.s

Internal resistance

The resistance of a source of e.m.f. which causes a loss in energy/ voltage as the charge passes through it

Terminal p.d.

The potential difference across an electrical power source (when I = 0, V = E)

Lost volts

The potential difference across the internal resistor of a source of e.m.f.

Progressive wave

An oscillation that travels through matter or a vacuum, transferring energy from one place to another, but not matter

Transverse wave

A wave in which the oscillations are perpendicular to the direction of energy transfer

Longitudinal wave

A wave in which the oscillations are parallel to the direction of energy transfer

Displacement

The distance between two points in phase on adjacent waves

Amplitude

The maximum displacement of a particle from the equilibrium position

Wavelength

The minimum distance between two points in phase in adjacent waves

Period

The time taken for one oscillation/ for one wave to move a full wavelength past a given point

Frequency

The number of wavelengths passing a given point per unit time

Wave speed

The distance travelled by a wave per unit time

Phase difference

The difference between the displacements of particles along a wave or the difference between the displacements of particles on different waves

Reflection

Occurs when a wave changes direction at a boundary between media, remaining in the original medium

Law of reflection

Angle of incidence = angle of reflection

Refraction

Occurs when a wave changes speed and bends as it passes into a new medium

Diffraction

When waves pass through a gap, or travel around an obstacle and spread out

Polaristaion

When the oscillations of a transverse wave are limited to one plane (same as direction of travel)

Intensity of a progressive wave

The radiant power passing through a surface per unit area

Critical angle

The angle of incidence at which light refracts at a 90° angle (travels along boundary)

Total internal reflection

When a wave strikes the boundary between two different media at a large angle and the entire wave is reflected (high > low n)

‘n’ for waves

refractive index

Principle of superposition of waves

When two waves meet at a point, the resultant displacements at that point is equal to the sum of the displacements of the individual waves

Interference

When two progressive waves pass through each other and superpose to produce a resultant wave

Coherence

When waves emitted from two sources have a constant phase difference

Path difference

The difference in the distance travelled by waves at a point

Constructive interference

Superposition of waves in phases giving a resultant wave of greater amplitude than the original wave (path dif = whole no wavelengths)

Destructive interference

Superposition of waves in anti-phase giving a resultant wave of smaller amplitude than the original waves (cancel) (path dif = odd no half wavelengths)

Stationary/ standing wave

When two progressive waves travelling in opposite directions overlap and superpose with no net transfer of energy (new wave has same frequency and amplitude as original wave)

Node

Position of minimum displacement on a stationary wave

Antinode

Position of maximum displacement on a stationary wave

Fundamental frequency

The lowest frequency at which an object can vibrate

Fundamental mode of vibration

The oscillation of a wave at its fundamental (natural) frequency

Photon

Quantum (packet) of energy of EM radiation (exhibit particle and wave like behaviour)

Work function

Minimum energy required to emit an electron from the surface of a metal

Threshold frequency

Minimum frequency of incident radiation required to emit an electron from the surface of a metal (in the photoelectric effect)

Electronvolt (eV)

Amount of KE gained when an electron is accelerated through a p.d. of 1V

Photoelectric effect

The emission of electrons from a metal surface when EM radiation of threshold frequency is incident on it.