Chapter 4 KEY INFO

Define electric current and 1 amp

Electric current

• The rate of flow of charge

1 amp

• 1 C passes per second

State the direction of convectional current and electron movement

Convectional Current - Positive to Negative

Electron Movement - Negative to Positive

State Kirchoff’s 1st Law

• The sum of currents entering a junction equals the sum of the currents leaving it

• Charge is conserved

Define Voltage and 1 volt

Voltage

• Energy transferred per unit charge

1 Volt

• 1 V is 1 J per 1 C

What is Ohmic Behaviour?

Current is directly proportional to Voltage

On an I-V Graph the gradient is constant

What happens to resistance of NTC thermistors when the temperature is changed

Temperature Up, Resistance Down. Vice Versa

State how conductors, semiconductors and insulators are different in terms of charge carrier density

Conductors - very high number density

Semiconductors - intermediate number density

Insulators - very low number density

State Kirchoff’s 2nd Law

The sum of the emf’s = the sum of the potential differences in a closed loop.

Energy is conserved

Define EMF and internal resistance of a cell

Emf - Energy transferred per unit charge from chemical to electrical energy inside the power source

Internal resistance - intrinsic resistance within a cell that causes voltage loss when current flows.

EMF and internal resistance on V-I graph

Y intercept - emf

Gradient = internal resistance (negative)

State the meaning of longitudinal and transverse waves

Longitudinal

• Particle oscillation is parallel to the direction of wave direction

Transverse

• Particle oscillation is perpendicular to the direction of wave direction

State what is unpolarised light and plane polarised light.

Unpolarised

• Oscillations occur in multiple random planes

Plane Polarised

• Oscillations occur in a single plane only

What stays the same and what changes when a wave is refracted?

Frequency - The Same

Wavelength and Speed - Changes

Conditions for Maximum diffraction

Size of the gap is similar or slightly larger than the wavelength of incident wave.

Define Coherence

Two monochromatic waves maintain a constant phase difference.

How does the fringe pattern change due to these conditions?

• Higher frequency wave

• Filament lamp

• Higher Frequency wave - Bright spots become closer

• Filament Lamp - Pattern ceases as light is no longer coherent

Principle of superposition

Total displacement at any point is the vector sum of the individual displacements of two or more waves that overlap

Conditions needed for constructive and destructive interference

Constructive Interference

• 0° (in phase)

• path difference of n wavelength

Destructive Interference

• 180° (completely out of phase)

• path difference of n + ½ wavelengths

What is a standing wave?

The interference of two same waves travelling in opposite directions, resulting in the formation of nodes and antinodes

These waves are formed by reflection or the overlap of coherent waves.

Phase relationship in a standing wave

At nodes, all points are in phase with ZERO amplitude

At antinodes, all points are antiphase.

Nodes and antinodes in open/closed pipes

open - open pipe: Antinodes at both open ends, nodes in between

closes - open pipe: Node at the closed end, anti node at the open end

Define a photon.

A quantum of electromagnetic energy

Wave - particle evidence

The photoelectric effect

Define Photoelectric emission

Stripping electrons off the surface of a metal when incident light is upon it.

Define Work Function

The minimum energy required to release an electron from the surface of a metal

Particle - wave behaviour

Electron diffraction

Explain the Electron Diffraction Experiment

• In an evacuated tube, electrons are shot through an electron gun.

• These electrons are diffracted by a thin graphite target

• Electrons produce visible light on a phosphorous screen