Studied by 18 people

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1

Speed

**How fast **you’re going with no regard to direction

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Velocity

**How fast **you’re going, but **also **with the **specified** direction

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*Equation: Avg. speed, Distance, Time*

v = s/t

Average speed = Distance moved/Time taken

[m/s] = [m]/[s]

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Acceleration

**How quickly **velocity is **changing**

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*Equation: Acceleration, Change in velocity, Time*

a = (v-u)/t

Acceleration = (Final velocity - initial velocity) / Time taken

[m/s²] = ([m/s]-[m/s]) / s

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*Equation: Final speed, Initial speed, Acceleration, Distance*

v² = u² + 2as

(Final velocity)² = (Initial velocity)² + (2 x Acceleration x Distance)

[m/s]² = [m/s]² + 2 x [m/s²] x [m]

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Distance-Time Graphs

**Gradient**at any point =**speed**of object**Flat**section =**stopped****Steeper**graph =**faster**speed**Curve**=**acceleration****Curve getting steeper**=**speeding up**(increasing gradient)**Levelling off curve**=**slowing down**(decreasing gradient)

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Velocity-Time graphs

**Gradient**=**acceleration****Flat**section =**steady**speed**Steeper**graph =**greater**acceleration/deceleration**Uphill**section =**acceleration****Downhill**section =**deceleration****Area**under any part of graph =**distance**travelled in that**time**interval**Curve**=**changing acceleration**

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Investigating motion

Set up apparatus as in diagram, holding car still just before light gate

Mark a

**line**on ramp to make sure car starts from**same point**each timeMeasure

**distance**between each light gate - need this to find car’s**average speed****Let go**of car just before light gate so it starts to roll down slopeLight gates should be connected to

**computer**

When car passes through each**light gate**, a beam of light is broken and**time**is recorded by**software****Repeat**experiment several times to get**average time**taken for car to reach each light gateUse these times and distances to find

**average speed**of car on ramp and average speed of car on runway - divide**distance between light gates**by average**time taken**for car to travel between gates

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Gravity

Gravity attracts **all **masses, but only noticeable when one of the masses is **very big**

This has **three** effects:

On surface of planet, makes things

**accelerate**towards**ground**Gives everything

**weight**Keeps

**planets**,**moons**,**satellites**in**orbit**

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Weight vs Mass

**Mass**is**amount of ‘stuff’**in object - same value**anywhere**in universe**Weight**is caused by**pull**of gravityObject has

**same**mass on**Earth**and**Moon**- but**different weight**1kg mass

**weighs less**on Moon (1.6N) than**Earth**(10N) because**force**of gravity pulling on it is**less**Weight is

**force**measured in**newtons****Mass**is**not**a force

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*Equation: Weight, Mass, Gravity*

W = mg

Weight = Mass x Gravitational field strength

[N] = [kg] / [N/kg]

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Force

A **push **or **pull**

Vector quantity with **size** + **direction**

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Gravity/Weight

When close to a planet this acts** straight downwards**

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Reaction force

Acts **perpendicular **to surface and away from it (if surface is **horizontal**, reaction force acts **straight upwards**)

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Electrostatic force

Between two **charged** objects

Direction depends on **type **of charge (**like **charges repel, **opposites** attract)

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Thrust

e.g. **push **or **pull** due to engine/rocket **speeding something up**

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Drag/air resistance/friction

**Slows the object down**

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Lift

e.g. due to **aeroplane wing**

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Tension

in a **rope **or **cable**

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Drawing the forces acting on a body

**Many forces**act on everything, but usually not noticed because they**balance out**Any object with

**weight**feels**reaction force**back from the surface it’s on

Otherwise it would just keep**falling**When an object

**moves**in**fluid**(air, water etc.), it feels**drag**in**opposite direction**to motion

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Friction

If an object has **no force** propelling it, it always **slows down and stops **due to **friction** (**force **that **opposes motion**)

To travel at **steady speed**, objects need **driving force** to **counteract **friction

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23

Static friction

Friction between **solid surfaces** which are **gripping**

Can be reduced by putting **lubricant** (**oil**/**grease**) between surfaces

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Sliding friction

Can be reduced by putting **lubricant** (**oil**/**grease**) between surfaces

Friction between **solids** often causes **wear **of two **surfaces** in contact

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Drag

Keeping shape of object **streamlined **(sports car, boat hull) reduces **drag in fluids**

Lorries + caravans have ‘**deflectors**’ to make them more streamlines + reduce drag

**Roof boxes** on cars spoil their streamlined shape so slow them down

For a given thrust, **higher drag** = **lower top speed** of car

**Opposite extreme** is **parachute** (need as high drag as possible)

In **fluid**, **friction always increases as speed increases**

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26

Newton’s **First **Law of Motion

As long as forces on object are **balanced**, it will **stay still**, or if already moving, it carries on at **same velocity**

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Newton’s **Second **Law of Motion

If there is **unbalanced force**, object **accelerates** in that direction

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*Equation: Force, Mass, Acceleration*

F = ma

Force = Mass x Acceleration

[N] = [kg] x [m/s²]

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Vector quantities

Have **size** and **direction**

e.g. force, velocity, acceleration, momentum

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Scalar quantities

**Only **size, **no direction**

e.g. mass, temperature, time, length

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Resultant force

When **multiple forces** act on object, you can find **resultant force** acting on object by **adding**/**subtracting** - need to know **size **of all **different forces** acting on object and their **direction**

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Terminal velocity

Frictional forces **increase** with **speed** - but only up to a **certain point**

When object first starts to fall, it has

**much more**force**accelerating**it than**resistance**slowing it downAs

**velocity increases**, resistance**builds up**Resistance force gradually

**reduces****acceleration**until**resistance****force**is**equal**to**accelerating force**

At this point, object can’t accelerate any more, it has reached**terminal velocity**

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Factors affecting terminal velocity

**Accelerating force**acting on**all falling objects**is**gravity**

All objects would accelerate at the same rate without**air resistance****Air resistance**causes things to fall at**diff speeds**, and**terminal velocity**of object is determined by its**drag**compared to its**weight**

Drag depends on**shape**and**area**

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Stopping distance

Distance covered in the time between driver **first spotting **a hazard and the car coming to **complete stop**

Stopping Distance = Thinking Distance + Braking Distance

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Factors affecting **thinking distance**

**Reaction time**- affected by**tiredness**,**drugs**,**alcohol**and**old age**

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Factors affecting **braking distance**

**Speed**-**faster**speed**= further**distance before stopping**Mass**of vehicle -**larger mass**=**longer time to stop****Quality of brakes**-**worn**/**faulty**brakes**increase**braking distance**Grip**- depends on**road surface**,**weather**conditions (e.g. icy),**tyres**

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Equation: *Pressure difference*

p = h x ρ x g

Pressure difference = Height x Density x Gravitational field strength

[Pa] = [m] x [kg/m³]

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Investigating how extension varies with applied force

Set up apparatus as in diagram

Measure

**length**of spring using mm ruler when**no load**is applied

Ensure ruler is**vertical**and measure spring at**eye level**(this is spring’s**natural length**)Add one mass at a time and allow spring to come to rest, then measure new

**length**of spring**Extension**= change in length from original length**Repeat**process until you have enough measurementsOnce done,

**repeat**experiment and calculate**average**value for length of spring for each applied weight**Repat**experiment using**metal wire**or**rubber band**instead of spring

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Hooke’s Law

**Extension** of stretched wire is **proportional** to **load**/**force**

Metal spring (or other object) also obeys Hooke’s law if a pair of **opposite forces** are applied to each end

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Force-extension graph

There’s a **limit **to force you can apply for Hooke’s law to stay true

**First part **of graph shows Hooke’s law being obeyed - straight-line relationship between force and extension

When force becomes great enough, graph starts to curve

If you **increase **force **past elastic limit **(marked E on graph), material is **permanently stretched**

When all force is removed, material will be longer than at the start

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Elastic behaviour

Ability of material to **recover **to **original shape **after **forces **causing **deformation **have been **removed**

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Electrical conductors

Materials that conduct charge easily - **current **can flow through

Usually **metals** e.g. copper + silver

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Electrical insulators

Don’t conduct charge very well - current can’t flow

e.g. plastic + rubber

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44

Series circuits

Components connected

**in a line**,**end to end**, between +ve and -ve of power supplyIf you remove/disconnect

**one**component, circuit is**broken**+ all**stop working****Not very useful**, only**a few things**are practically connected in series e.g. fairy lights

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Voltage in series circuit

There’s a bigger

**supply p.d.**when more cells are connected in seriesTotal

**p.d.**of supply is**shared**between componentsp.d. of each component depends on its

**resistance**

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Current in series circuit

**Current same everywhere**, I₁ = I₂Size of current depends on

**total p.d.**and**total resistance**of circuit

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Resistance in series circuit

**Total resistance**of circuit depends on**number**+**type**of**components**Total resistance is

**sum**of resistance of**each component**in circuit

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48

Parallel circuits

Each component is

**separately**connected to +ve and -ve of**supply**If you remove/disconnect

**one**component, others are**hardly affected**This is how

**most**things are connected

e.g.**cars**and**household electrics**

Each**light switch**in your house is part of branch of parallel circuit (turns**one**light on/off)Everyday circuits often contain

**mixture**of series and parallel parts - rules of**series**circuits apply to components on**same branch**

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Current in parallel circuit

**Current shared**between**branches****Total current**flowing around circuit =**total**of all currents through**separate components**There are

**junctions**where current**splits**or**rejoins**Total current going

**into**junction = total current**leaving**it**Current**through branch depends on**resistance**, higher resistance = lower current

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Voltage in parallel circuit

**P.d.**is**same**across all branches, V₁ = V₂

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Resistance in parallel circuit

**Total resistance**of circuit**decreases**if you add second resistor in parallel

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**Wire **voltage-current characteristics

Current through **wire** is **proportional to voltage**

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**Resistor **voltage-current characteristics

Current through **resistor **is **proportional to voltage**

**Different resistors **have different **resistances**

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**Metal filament lamp **voltage-current characteristics

As **temp **of metal filament **increases**, **resistance increases**

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**Diode **voltage-current characteristics

Current only flows through diode **in one direction**

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Ammeter

Measures

**current**(in**amps**) through componentMust be placed in

**series**anywhere in**main circuit**

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Voltmeter

Measures

**voltage**(in**volts**) across componentMust be placed in

**parallel**around**component**

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Investigating V-I characteristics

**Component**,**ammeter**and**variable resistor**are in**series**, so can be put in**any order****Voltmeter**must be placed in**parallel**around**component under test**As you

**vary variable resistor**, it alters**current**flowing through circuitAllowing you to take

**pairs of readings**from**ammeter**and**voltmeter**

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Effect of changing resistance on current

**More resistance** = **less current**

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LDR

Changes resistance depending on how much light it receives

In

**bright light**, resistance**falls**In

**darkness**, resistance is**highest**Useful for various

**electronic circuits**e.g.**burglar detectors**

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Thermistor

Temperature-dependent resistor

**Hot**= resistance**drops****Cool**= resistance**increases**Useful for

**temperature detectors**e.g.**car engine**temp sensors, thermostats

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LED

**Light-emitting diodes**emit light when current flows through them in forward directionUsed for numbers on

**digital clocks**and**traffic lights**Unlike light bulb, don’t have filament that can burn out

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LEDs and lamps can be used to…

indicate presence of **current** in circuit

Often used in appliances to show they’re switched on

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Equation: *Voltage, Current and Resistance*

V = IR

Voltage = Current x Resistance

[V] = [A] x [Ω]

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Current

Rate of **flow **of **charge** around a circuit

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Equation**: ***Charge, Current and Time*

Q = It

Charge = Current x Time

[C] = [I] x [s]

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In solid metal conductors, current is…

a flow of **negatively charged electrons**

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68

Plugs

Have

**three**wires -**live**,**neutral**,**earth**Only

**live**and**neutral wires**usually needed, but**earth wire**stops you getting hurt if something goes wrong**LIVE WIRE**alternates between**HIGH +VE AND -VE VOLTAGE**of**230V****NEUTRAL WIRE**always at**0V**Electricity normally flows in through live and neutral wire

**EARTH WIRE**and fuse are just for**safety**

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Double insulation

If appliance has **plastic casing** and no metal parts **showing**, it’s said to be **double insulated**

Plastic is **insulator**, so stops current flowing - meaning you can’t get a shock

Anything with **double insulation doesn’t need earth wire**

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Earthing and fuses

If fault develops in which

**live**touches**metal case**, then because case is**earthed**,**big current**flows through**live wire**,**case**and**earth wire****Surge**in current**melts the fuse**,**cutting off**the**live supply**This

**isolates**the**whole appliance**, making it**impossible**to get**electric shock**from case

Also prevents risk of**fire**caused by heating effect of large current

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Circuit breakers

**Protect**circuit from**damage**if**too much**current flowsWhen

**circuit breakers**detect**surge**in**current**, they**break**circuit by**opening**a**switch**Circuit breaker can easily be

**reset**by flicking a**switch**on the device

This makes them more convenient than fuses (have to be**replaced**once melted)

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Heating effect in resistors

When there is **electrical current** in **resistor**, there is **energy transfer** which heats resistor

Because **electrons collide with ions** in lattice that make up resistor as they flow through it

This gives ions **energy**, causing them to **vibrate** and **heat up**

**Heating effect** increases resistor’s **resistance** - so **less current** flows

Heating effect can cause **components** in circuit to **melt** - so circuit **stops** working

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Use of heating effect in resistors

**Toasters **contain coil of wire with very **high **resistance

When current passes through coil, **temp increases** so much that it **glows **and emits IR (heat) radiation which **cooks** bread

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Equation: *Power, Current and Voltage*

P = IV

Power = Current x Voltage

[W] = [A] x [V]

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Fuse ratings

**Fuses**have**current ratings**and should be rated as near as possible but**just higher**than the**normal operating current**To work out the

**fuse**needed, you need to work out the**current**that item normally uses

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Equation: *Energy, Current, Voltage and Time*

E = IVt

Energy transferred = Current x Voltage x Time

[J] = [A] x [V] x [s]

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Alternating current (a.c.)

Current is **constantly** changing direction

Used for **mains supply**, e.g. UK mains supply is approx. **230V**

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Direct current (d.c.)

Current keeps flowing in **same direction**

Used in cells and batteries

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Voltage

**Energy transferred **per **unit charge passed**

**One volt** = **one joule** per **coulomb**

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Equation: *Energy, Charge and Voltage*

E = QV

Energy transferred = Charge x Voltage

[J] = [C] x [V]

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81

Longitudinal wave

Vibrations are along **same direction** as energy transfer

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Transverse wave

Vibrations are **perpendicular **(at 90ᵒ) to **direction of energy transfer**

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Amplitude

**Height **of wave (from **rest** to **crest**)

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Frequency (f)

Number of **complete waves per second** (passing a certain point)

Measured in **hertz** (Hz)

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Wavelength (λ)

Distance from one peak to the next

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Period of wave (T)

**Time taken** (in **s**) for **one complete wave** to pass a point

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Wavefront

Imaginary **planes** that cut across multiple waves, connecting points on adjacent waves which are **vibrating together**

Distance between each wavefront = **one wavelength**

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Waves transfer…

**energy** and **info** without transferring **matter**

e.g. **microwaves** in an oven make things **warm up** - energy transferred to **food **you’re cooking

Waves can be used as **signals **to **transfer info** from one place to another

e.g. **radio waves **travelling through **air**

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Equation: *Wave speed, frequency and wavelength*

v = fλ

Wave speed = Frequency x Wavelength

[m/s] = [Hz] x [m]

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Equation: *Frequency, Time period *

f = 1/T

Frequency = 1/time

[Hz] = 1/[s]

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Doppler effect

Waves produced by source which is moving

**towards**/**away from**observer have**diff wavelength**than they would if source was**stationary**Because

**wave speed**is**constant**, so if source is moving, it ‘catches up’ to waves in front

Causes wavefronts to**bunch up**in front of moving source and**spread out**behind it**Frequency**of wave from source moving**towards**you is**higher**and**wavelength shorter**than wave produced by source**Frequency**of wave from source moving**away from**you is**lower**and**wavelength longer**than wave produced by source

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All waves can be…

reflected and refracted

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Sound waves

**Longitudinal **waves caused by **vibrating objects**

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Light waves are…

**transverse **waves

that can be **reflected** and **refracted**

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Law of reflection

Angle of incidence = Angle of reflection

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Ray diagrams for reflected waves

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Refraction

Waves travel at **different speeds** in substances with **different densities**

Sound waves travel **faster **in **denser **substances

When a wave crosses a boundary between two substances (e.g. glass to air), it **changes speed**

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Ray diagrams for refracted waves

Show the **path **that a **wave **travels

Draw

**boundary**between two materials and the**normal**(a line perpendicular to boundary)Draw

**incident ray**that**meets normal**at**boundary**Angle

**between ray**and**normal**=**angle of incidence**Draw

**refracted ray**on other side of boundary

If second material is**denser**than first, refracted ray**bends towards**normal**Angle**between**refracted**ray and**normal**(angle of**refraction**) is**smaller**than**angle of incidence**If second material is

**less dense**, angle of refraction is**larger**than angle of incidence

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99

Investigating refraction

Place glass block on piece of paper, and carefully draw around rectangular perspex block using pencil

Switch on ray box and direct beam of light at side face of block

Mark on paper:

Point on ray close to ray box

Point where ray enters block

Point where ray exits block

Point on exit light ray which is 5cm away from block

Draw dashed line normal (at right angles) to outline of block where points are

Remove block and join points marked with 3 straight lines

Replace block within its outline and repeat process for ray striking block at different angle

Repeat procedure for each shape of perspex block (semi-circular and prism)

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Rectangular block

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