AS Unit 2

Question 1

What is electric current?

Answer 1

The rate of flow of electric charge. Unit: A (Ampere)

I = ΔQ/ΔT

Question 2

How is efficiency defined?

Answer 2

% Efficiency = 100 x useful work (or energy) out / work (or energy) put in

Unit: none

Question 3

What is potential difference (pd)?

Answer 3

The energy converted from electrical potential energy to another form per coulomb of charge. Unit: V (Volt)

V = J/C

Question 4

What does Ohm’s law state?

Answer 4

The current in a metal wire at constant temperature is proportional to the pd across it.

Question 5

How is electrical resistance (R) calculated?

Answer 5

R = V / I

Unit: Ohm (Ω) = VA

Question 6

What is the formula for resistivity?

Answer 6

R = ρL / A

R is resistanace, L is length, A is cross-sectional area.

ρ is resistivity, Unit: Ω m

Question 7

What is the superconducting transition temperature (Te)?

Answer 7

The temperature at which a material suddenly loses all electrical resistance and becomes superconducting.

Question 8

What is the law of conservation of charge?

Answer 8

Electric charge cannot be created or destroyed. Charges can neutralize each other.

Question 9

What is emf (electromotive force)?

Answer 9

The energy converted from another form to electrical potential energy per coulomb of charge. Unit: V

Example: chemical to electrical energy

Question 10

What is a progressive wave?

Answer 10

A pattern of disturbances traveling through a medium and carrying energy with it.

Question 11

Define a transverse wave.

Answer 11

A wave where the particle oscillations are at right angles to the direction of wave propagation.

Question 12

Define a longitudinal wave.

Answer 12

A wave where the particle oscillations are in line with the direction of wave propagation.

Question 13

What is a polarised wave?

Answer 13

A transverse wave in which particle oscillations occur in only one direction at right angles to wave propagation.

Question 14

What does it mean for waves to be in phase?

Answer 14

Waves are in phase if they have the same frequency and are at the same point in their cycles at the same time.

Question 15

How is the wavelength of a progressive wave defined?

Answer 15

The minimum distance between two points on the wave oscillating in phase, measured along the direction of propagation.

Question 16

What is the frequency of a wave?

Answer 16

The number of cycles of a wave that pass a given point in one second
or
the number of cycles of oscillation per second performed by any particle in the medium through which the wave is passing.

Frequency is often measured in Hertz (Hz).

Question 17

What is the speed of a wave?

Answer 17

The distance that the wave profile moves per unit time.

Speed can be calculated using the formula: speed = frequency × wavelength.

Question 18

What is diffraction?

Answer 18

The spreading out of waves when they meet obstacles, such as the edges of a slit, with some of the wave’s energy traveling into the geometrical shadows of the obstacles.

Diffraction is more pronounced when the size of the obstacle is comparable to the wavelength of the wave.

Question 19

What does the principle of superposition state?

Answer 19

If waves from two sources occupy the same region, the total displacement at any one point is the vector sum of their individual displacements at that point.

This principle applies to all types of waves, including sound and light waves.

Question 20

Define phase difference

Answer 20

The difference in position of two points within a cycle of oscillation, given as a fraction of the cycle or as an angle, where one whole cycle is 2π or 360°.

Phase difference indicates how far one wave is ahead or behind another.

Question 21

What is coherence in wave mechanics?

Answer 21

Waves or wave sources that have a constant phase difference between them and therefore must have the same frequency.

Coherent sources are crucial for interference patterns.

Question 22

What is a stationary (or standing) wave?

Answer 22

A pattern of disturbances in a medium where energy is not propagated, with zero amplitude at nodes and maximum amplitude at antinodes.

Stationary waves are formed by the interference of two waves traveling in opposite directions.

Question 23

Define the refractive index, n.

Answer 23

The ratio of the sine of the angle of incidence to the sine of the angle of refraction at the boundary between two media.

The refractive index indicates how much light slows down in a medium compared to a vacuum.

Question 24

What is Snell’s law?

Answer 24

n1 sin θ1 = n2 sin θ2, where θ1 and θ2 are angles to the normal for light passing between two media, and n1 and n2 are the refractive indices of those media.

Snell’s law describes how light bends when it enters a different medium.

Question 25

What is the critical angle, C?

Answer 25

The largest angle of incidence for which refraction can occur when light approaches the boundary between two media from the ‘slower’ medium. ## footnote Beyond this angle, total internal reflection occurs.

Question 26

What is the photoelectric effect?

Answer 26

The emission of electrons from a surface when light or ultraviolet radiation of short enough wavelength falls on it. ## footnote This effect demonstrates the particle nature of light.

Question 27

Define work function.

Answer 27

The minimum energy needed to remove an electron from the surface of a material, measured in Joules (J) or electron volts (eV). ## footnote The work function varies for different materials.

Question 28

What is ionization energy?

Answer 28

The minimum energy needed to remove an electron from an atom in its ground state, measured in Joules (J). ## footnote Ionization energy is a key concept in atomic physics.

Question 29

What is stimulated emission?

Answer 29

The emission of a photon from an excited atom triggered by a passing photon of energy equal to the energy gap between the excited state and a state of lower energy. ## footnote The emitted photon has the same frequency, phase, direction of travel, and polarization as the passing photon.

Question 30

What is population inversion?

Answer 30

A situation where a higher energy state in an atomic system is more heavily populated than a lower energy state of the same system. ## footnote Population inversion is essential for laser operation.

Question 31

What is pumping in the context of lasers

Answer 31

Feeding energy into the amplifying medium of a laser to produce a population inversion. ## footnote Pumping can be achieved through various methods, including optical or electrical excitation.

Question 32

Fill in the blank: The energy transferred when an electron moves between two points with a potential difference of 1 V is called _______.

Answer 32

Electron volt (eV) ## footnote 1 eV = 1.60 x 10^-19 J.