Module 4 - Equations

Question 1

Current definition equation

4.1 - Charge and current

Answer 1

I = ΔQ/Δt

ΔQ - Charge transferred (C)
t - time (s)

I = Current (A)

Question 2

Kirchhoff’s first law

4.1 - Charge and current

Answer 2

ΣIᵢₙ = ΣIₒᵤₜ

Question 3

Mean drift velocity

4.1 - Charge and current

Answer 3

I = Anev

I - current (A)
A - cross-sectional area of conductor (m²)
n - number density (m⁻³)
e - charge of each charge carrier (C)
v - drift velocity (ms⁻¹)

Question 4

Potential difference defintion

4.2 - Energy, power and resistance

Answer 4

V = W/Q

V - potential difference (V)
W - Electrical energy transfered (J)
Q - Charge (C)

Question 5

Electromotive force

4.2 - Energy, power and resistance

Answer 5

ε = W/Q

ε - electromotive force (V)
W - Electrical energy provided (J)
Q - Charge (C)

Question 6

Electron gun equation

4.2 - Energy, power and resistance

Answer 6

QV = ½mv²

Q - Charge of particle (C)’
V - voltage (V)
m - mass of particle (kg)
v - velocity (ms⁻¹)

Question 7

Resistance definition

4.2 - Energy, power and resistance

Answer 7

R = V/I

R - Resistance (Ω)
V - voltage (V)
I - Current (A)

Question 8

Resistivity

4.2 - Energy, power and resistance

Answer 8

R = ρL/A

R - resistance (Ω)
ρ - resistivity (Ωm)
L - conductor length (m)
A - cross sectional area of conductor (ms⁻¹)

Question 9

Electricial Power, 3 of them

4.2 - Energy, power and resistance

Answer 9

P = VI
P = I²R
P = V²/R

P - Power (W)
V - Voltage (V)
I - Current (A)
R - Resistance (Ω)

Question 10

Kirchoffs second law

4.3 - Electric circuits

Answer 10

Σε = ΣV

The sum of the emfs equals the sum of potential differences around a closed loop

Question 11

Internal Resistance

4.3 - Electric circuits

Answer 11

ε = V + Ir
or
ε = I(R + r)

ε - emf (V)
V - terminal potential difference (V)
I - Current (A)
r - internal resistance (Ω)
R - Load resistance (Ω)

Question 12

Potential dividers

4.3 - Electric circuits

Answer 12

V₁/V₂ = R₁/R₂
and
Vₒᵤₜ = (R₂/(R₁+R₂)) x Vᵢₙ

Question 13

Wave equation

4.4 - Waves

Answer 13

v = fλ

v = wave speed (ms⁻¹)
f = frequency (Hz)
λ = wavelength (m)

Question 14

Frequency

4.4 - Waves

Answer 14

f = 1/t

f - Frequency (Hz)
T - time period (s)

Question 15

Light intensity

4.4 - Waves

Answer 15

I = P/A
or
I = P/4πr²

I - Intensity (Wm⁻²)
P - Power (W)
A - Area of which power is spread (m²)
r - distance from energy source (m)

Question 16

Relationship between radiation intensity and amplitude

4.4 - Waves

Answer 16

Radiation intensity ∝ (Amplitude)²

Question 17

Refractive index definition equation

4.4 - Waves

Answer 17

n = c/v

n - refractive index of the medium
c - speed of light in a vacuum (ms⁻¹)
v - speed of light in the medium (ms⁻¹)

Question 18

Snells law

4.4 - Waves

Answer 18

n₁ sin𝜃₁ = n₂ sin𝜃₂

n - refractive index of the medium
𝜃 - angle between normal and the ray (°)

Question 19

Critical angle

4.4 - Waves

Answer 19

Sin C = 1/n

C - Critical angle of the medium (°)
n - refractive index of the medium

Question 20

Double slit equation

4.4 - Waves

Answer 20

λ = ax/D

λ - wavelength (m)
a - separation of slits (m)
x - distance between the central maximum and the first order maximum (m)
D - distance between slits and screen (m)

Question 21

Diffraction grating equation

4.4 - Waves

Answer 21

nλ = d sin𝜃

n - order of maximum
λ - wavelength of light (m)
d - slit separation (m)
𝜃 - angle at which the nᵗʰ maximum is observed (°)

Question 22

Photon energy

4.5 - Quantum physics

Answer 22

E = hf
or
E = hc/λ

E - Photon energy (J)
h - planck constnat (Js)
f - frequency (Hz)
c - speed of light (ms⁻¹)
λ - wavelength (m)

Question 23

Photoelectric effect equation

4.5 - Quantum physics

Answer 23

hf = ɸ + KEₘₐₓ

hf - incident photon energy (J)
ɸ - work function for the metal (J)
KEₘₐₓ - maximum KE of photoelectrons (J)

Question 24

De broglie wavelength

4.5 - Quantum physics

Answer 24

λ = h/p
or
λ = h/√2mKE

λ - de broglie wavelength (m)
h - planck constant (Js)
p - momentum (kgms⁻¹)
m - mass (kg)
KE - Kinetic energy (J)