3.6 Use the relationship between frequency and time period

Frequency = 1 / period

Period = 1 / frequency


Frequency in Hz (hertz)
Period in s (seconds)

3.5 Know and use the relationship between the speed, frequency and wavelength of a wave:

Speed = frequency x wavelength
V = f x λ

Speed in m/s
Frequency in Hz
Wavelength in m

6.20 Know and use the relationship: input power = output power for 100% efficiency

VPIP =VSIS


Voltage primary x current primary = voltage secondary x current secondary

Voltage in volts (v)
Current in amps (A)

6.19 Know and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer:

^Vp/_Vs = ^Np/<sub>Ns
Voltage primary ÷ voltage secondary = Number of coils in primary ÷ number of coils in secondary

Number of coils has no units
Voltage is in volts</sub>

1.35 Use the relationship between orbital speed, orbital radius and time period

0. 
   
1. orbital speed = 2 x π x r / T
2. ( 2 x pi x radius ÷ time)

Orbital speed in m/s

Radius in m

Time in sec

2.16 Know and use the relationship between charge, current and time:

Charge = Current x Time
Q = I x T

Q measured in coulombs (C)
I measured in amperes (A )
T is measured in seconds (sec)

2.14 Know and use the relationship between voltage, current and resistance:

IMPORTANT EQUATION!!

Voltage = Current x Resistance
V = I x R

Voltage measured in volts (V)
Current measured in amps (A)
Resistance measured in ohms (Ω)

You will need to re-arrange this equation a lot so keep this in mind:

Figure 1

2.6 Use the relationship between energy transferred, current, voltage and time

E = I x T x V
(way to remember it is E = ITV)
Energy transferred = Current x Voltage x Time

Energy is measured in Joules (J)
Current is measured in amperes (A)
Voltage is measured in volts (V)
Time is measured in seconds (sec)

Converting...
1 A = 0.001 kilo amps (divide by 1000)
1A = 0.000001 mega amps (divide by 1 million; 1000000)
1A = 1000 miliamps

(If you understand, don't look at the one below because it might confuzzle you)


In other words...
1 KILO amp = 1000 amps
1 MEGA amp = 1000000 amps (that's a million)
I MILI amp = 0.001

Same applies to all else :)

2.5 Know and use the relationship: power = current × voltage and apply the relationship to the selection of appropriate fuses

Fairly self explanatory.

Power = Current x Voltage 
P = I x V

P measured in watts (W)
I measured in amperes (A)
V measured in volts (V)

!!WARNING!!
I represents current. Although A is the symbol for the units, it does not represent current in an equation. If you write P = A x V in an exam you will get marked down because it is wrong.

Power is the rate of energy transferred. Fuses will usually tell you the voltage and current of the device, and from this, the power can be worked out

4.12 Know and use the relationship between kinetic energy, mass and speed

Kinetic Energy = 1/2 x Mass x Velocity²

KE = 1/2 x M x V²

Kinetic Energy - J
Mass - kg
Velocity - m/s

4.11 Know and use the relationship: gravitational potential energy = mass × g × height

Gravitational Potential Energy = Mass x Gravity x Height

GPE = M x G x H

Mass - kg
Gravity - 10 on earth (N/kg)
Height - m
GPE - J

4. 10 Understand that work done is equal to energy transferred

Work done = Energy Transferred

I.e. if the work done is 200J, and the question asks you, "what is the energy transferred?", the answer is 200J.

4.9 Know and use the relationship between work, force and distance moved in the direction of the force

Work done = Force x Distance

Force must be parallel to distance (otherwise you'll be working out the moment, and since there's no pivot, it would be wrong!)

W = F x D

Work done - J 
Force - N
Distance - m

1.16 Know and use the relationship between weight, mass and gravity

Weight = Mass x Gravity

YOUR WEIGHT IS NOT THE SAME AS YOUR MASS!

Your mass never changes - if your mass is 50 kg, you will still have a mass of 50 kg on the moon, on mars, anywhere. Your weight does change, because it is the effect of gravity on your body - this changes from planet to planet. And in space, of course, your weight = almost 0

W = M x G

Weight is a force, so it's measured in newtons. 
Mass ~ Kg
Gravity ~ 10 on Earth (units are mostly irrelevant, but if you really want to know, it's N/kg)

Fun fact, by Annabel:
The reason the unit for gravity is N/kg is because if you rearrange this equation so that gravity is the subject is becomes:
gravity = weight ÷ mass
which, in terms of units is gravity = N/kg

1.15 Know and use the relationship between unbalanced force, mass and acceleration:

Force = mass x acceleration

F = M x A

Mass - Kg
Force - N
Acceleration - m/s²

1.8 Determine the distance travelled from the area between a velocity-time graph and the time axis

Distance travelled = Area under the graph

Eg. in figure 1, you'd calculate the area of triangles A and C, as well as the area of rectangle B. So:
A = 0.5 x B x H
= 0.5 x 10 x 20
= 100m
B = B x H
= 20 x 20
= 400m
C = 0.5 x B x H
= 0.5 x 40 x 20
= 400m

Add everything ~400 + 400 + 100 = 900m

Figure 1

1.7 Determine acceleration from the gradient of a velocity-time graph

Acceleration = gradient of graph



Gradient = Rise ÷ Run
[Change in y (rise) ÷ change in x (run)]

In figure 1, the rise would be the dotted line and the run would be how far it is, i.e. from 2 to 6 on the graph below. Let's say that each dash on the y axis represents 1 (i.e. the scale goes 1, 2, 3, 4 etc)

So, if you were to calculate the acceleration:
G = rise ÷ run
= 4 ÷ 5
= 0.8 m/s^2

Figure 1

1.5 know and use the relationship between acceleration, velocity and time

Acceleration = (Final velocity - Initial velocity) ÷ time

Acc. = (v - u) ÷ time

Velocity - m/s
Time - seconds
Acceleration -  m/s²

1.3 Know and use the relationship between average speed, distance moved and time

Average speed = Distance moved ÷ Time

S = D ÷ T

Velocity = Distance moved ÷ Time

V = D ÷ T

Velocity/speed - m/s
Distance - m
Time - seconds

4.4 Know and use the relationship between useful energy output, total energy input and efficiency

Efficiency = useful energy out ÷ total energy in (x 100)

Efficiency - %
Energy - J (joules)

Eg: If you have a lightbulb and it is "fed" 100J of energy, of which 10J are transferred into light energy and the rest is wasted as heat energy, what is the efficiency of the bulb?

Eff = E. useful out ÷ E. in
= 10 ÷ 100
= 0.1 x 100
= 10% efficient 

Conclusion: The poor person that bought this light bulb is going to have a very hot house/office/building and is going to have an enormous electricity bill. Also, it's a waste of money. And bad for the environment.
(don't write that [this "conclusion"] in your exam - the examiner probably won't find it funny.)