4PH1 Physics

Mass unit

kilogram (kg)

How to choose a fuse

find the current (I = P/V), above the normal operating current,

Too small → blows during normal use

Too large → doesn’t protect the device

In a series circuit the current is

the same everywhere

How does current depends on voltage

I = V /R

If voltage increases - current increases

if voltage decreases - current decreases

Current & Voltage: what is the affect of the number of components?

Adding more components - total resistance increases

and if there is a higher resistance, the current decreases

Rtotal​=R1​+R2​+R3​+...

In a block of wood / different types of surfaces, explain why masses are kept constant

because it is a controlled variable + to keep a fair test.

what is a moment?

• A moment is the turning effect of a force around a pivot.

• Formula: Moment = Force × Perpendicular distance from pivot

• Unit: Newton-metre (N·m)

when does light bend towards the normal?

• Light bends towards the normal when it slows down.

• This happens when it passes from a less dense medium to a more dense medium

Parallel Current

total current = sum of branch currents.

Where should a voltmeter be placed on a circuit diagram

parallel across the component being measured

Series Circuit Advs + dis

Simple to connect and uses fewer components.

If one component breaks, the whole circuit stops working.

When you see an object move in the opposite direction to another action, what should you think?

Think Newton’s Third Law (action-reaction):

• Every force has an equal and opposite force.

• Identify:

  • Action: what force is applied

  • Reaction: the opposite response

• Check for low friction if the motion is noticeable (ice, air, smooth surface).

Similarities between EM waves

• All transfer energy without transferring matter.

• All travel at the same speed in a vacuum (~3 × 10⁸ m/s).

• All are transverse waves (electric and magnetic fields are perpendicular to each other and to the direction of wave travel).

• All can reflect, refract, and diffract.

Differences between EM waves

• Wavelength: Different EM waves have different wavelengths (radio waves > microwaves > infrared > visible light > ultraviolet > X-rays > gamma rays).

• Frequency: Higher frequency waves carry more energy.

• Energy: Energy increases with frequency (E = hf).

• Uses: Each type has different applications (e.g., radio waves for communication, X-rays for medical imaging).

• Hazards: Some EM waves are more harmful (e.g., X-rays and gamma rays are ionising; visible light and radio waves are non-ionising).

In terms of electrons, whats the difference between conductors and insulators?

Electrons are free to move, allowing electric current to flow easily (e.g., metals like copper).

Electrons are tightly bound to atoms, so electric current cannot flow easily (e.g., rubber, plastic).

Parallel Circuit Advs + dis

If one component breaks, the rest still work.
More complex to connect and uses more wiring.

what is a resistor?

component in a circuit that provides resistance, limiting the flow of electric current.
It is used to control current and protect components.

(e) what is resistance in electricity?

(e) opposition to the flow of electric current in a circuit.

formula for resistance

R = V / I

Length unit

metre (m)

Time unit

second (s)

Speed unit

metre per second (m/s)

Acceleration unit

metre per second squared (m/s²)

Force unit

newton (N)

Gravitational field strength unit

newton per kilogram (N/kg)

What is 1 newton equal to?

1 N = 1 kg·m/s²

Unit of work/energy

newton metre (N·m)

Unit of momentum

kilogram metre per second (kg·m/s)

What does a distance-time graph show?

distance travelled over time

What does the gradient represent on a distance-time graph?

speed

(Dt) Straight line means

constant speed

(Dt) Horizontal line means

object is stationary

(Dt) Curve getting steeper means

accelerating

(Dt) Curve flattening means

decelerating

(Dt) Steeper gradient means

higher speed

Formula for average speed

speed = distance ÷ time

Distance formula (avg speed)

distance = speed × time

Time formula (avg speed)

time = distance ÷ speed

Unit of speed

m/s

What is measured in a motion practical?

distance and time

Equipment used - during a motion practical

stopwatch, ruler/measuring tape

Why repeat readings? motion practical

to calculate a reliable average

How to reduce error motion practical

repeat, use clear markers, reduce reaction time

Main calculation in motion practical

speed = distance ÷ time

Acceleration formula from v = u + at

a = (v − u) ÷ t

What is acceleration?

rate of change of velocity

Unit of acceleration

m/s²

Final velocity formula (when time is given)

v = u + at

Initial velocity formula (when time is given)

u = v − at

Time formula v = u + at

t = (v − u) ÷ a

Positive acceleration means

speeding up

Negative acceleration means

slowing down

What does a velocity-time graph show?

velocity over time

(Vt) Gradient represents

acceleration

(Vt) Horizontal line means

constant velocity

(Vt) Sloping up means

acceleration

(Vt) Sloping down means

deceleration

(Vt) Curved line means

changing acceleration

(Vt) Area under graph represents

distance travelled

Formula for acceleration from graph

a = Δv ÷ Δt

What is Δv?

change in velocity

What is Δt?

change in time

(Vt) Steeper gradient means

greater acceleration

(Vt) Negative gradient means

negative acceleration

Distance from v-t graph

area under the graph

Rectangle area

base × height

Triangle area

½ × base × height

Trapezium area

½ × (a + b) × height

Area above axis means

positive distance

Area below axis means

opposite direction

Main formula (When time is not given)

v² = u² + 2as

When to use this formula: v² = u² + 2as

when time is not given

Distance formula: v² = u² + 2as

s = (v² − u²) ÷ (2a)

Acceleration formula: v² = u² + 2as

a = (v² − u²) ÷ (2s)

Final velocity formula: s = (v² − u²) ÷ (2a)

v = √(u² + 2as)

Initial velocity formula: s = (v² − u²) ÷ (2a)

u = √(v² − 2as)

What each symbol means: v² = u² + 2as

v = final, u = initial, a = acceleration, s = distance

Gradient of distance-time graph gives

speed

Gradient of velocity-time graph gives

acceleration

Area under velocity-time graph gives

distance

What can a force change?

Speed, direction, shape

Balanced vs unbalanced forces

Balanced = no change in motion; Unbalanced = acceleration

Types of forces (1.12)

Contact = require touching; Non-contact = act at a distance

Examples of contact forces

Friction, air resistance, tension, normal contact force, upthrust

Examples of non-contact forces

Gravitational, electrostatic, magnetic

Scalars vs Vectors (1.13)

Scalar quantity has magnitude only

vector quantity has magnitude and direction

Examples of scalars

speed, distance, time, mass, energy

Examples of vectors

velocity, displacement, acceleration, force

Is force a scalar or vector?

It is a vector, has magnitude + direction

How are forces represented?

arrows (length = size, direction = direction)

Resultant force (1.15)

Forces in same direction

Added together

Forces in opposite directions

What to do? Subtract; direction of larger force

Resultant force = 0 meaning

What does it mean? Balanced forces, no acceleration

Friction is what? (1.16)

Force that opposes motion between surfaces

Effect of friction

Slows objects, produces heat

Force formula

F = m × a