# Physics; Modules 4, 5, 6

Key bits of information you will need to know for the exam. Using the information on the card and testing your friends helps a lot.

- Created by: Robyn
- Created on: 07-01-12 19:00

## Velocity and Calculating Speed (P4)

**Velocity** tells you an objects...

**speed****direction**of travel

The direction can also be ** positive** or

**. The idea is used when describing distance;**

*negative*- changes in distance in one direction are positive
- in the opposite direction they're negative.

To calculate **speed**, you need to know...

- the
**distance**travelled - the
**time**it took to travel

The formula is...

**Speed = distance travelled/time**

The speed of an object at a particular point in time is called the **instantaneous speed**.

## Distance-Time and Velocity-TIme Graphs (P4)

**Distance-Time Graphs**

The slope, or gradient of a distance-time graph is a measure of the distance travelled over a certain amount of time.

A **straight line** shows that there is **no movement**.

A **straight diagonal line** shows there is movement at a **constant speed**.

**Velocity-Time Graphs**

The gradient of a velocity-time graph shows how quickly an object is increasing in speed.

A **straight line** shows that there is movement at a **constant speed** - unless it is 0 m/s (or which ever unit), then the object is stationary.

An **upwards diagonal line** shows **acceleration**, **downwards** shows **decelleration**.

## Forces (P4)

A force occurs when two objects interact. The forces in an **interaction pair** are...

**equal**in size**opposite**in direction.

When an object is resting on a surface...

- the object is pulled down by gravity
- and the surfaces pushes up on the object with an equal force (
**reaction of the surface**)

When two objects slide past one another, both objects experience a force which tries to stop them moving; **friction**.

If more than one force acts on an object, they will **add** up in they are acting in the **same** direction. Or they will **subtract** if they are acting in **opposite** directions. This is called the **resultant force**.

## Momentum (P4)

**Momentum** is a measure of the motion of an object.

The formula is... **momentum = mass x velocity**

The extent of the change in momentum depends on...

- the size of the resultant force
- the length of time the force is acting on the object

The formula is... **change in momentum = resultant force x time the force acts for**

## Energy (P4)

A moving object has kinetic energy. The amount depends on an object's...

- mass
- velocity

**Kinetic energy = 0.5 x mass x velocity²**

**Work** is done by a force to move an object, resulting in **transfer of energy**, in this process the total amount of energy remains the same.

**Change in Energy = Work done**

**Work done by a force = force x distance**

When an object is lifted above the ground...

- work is done by the lifting force
- the object has potential work to do when it falls.

**Change in gravitational potential energy = weight x veritcal height difference**

## Current and Potential Difference (P5)

**Current** = flow of charge measure in amperes

Direct current - flows in the same direction

Alternating current - constantly changes direction

**Potential difference** = voltage - measure in volts

Greater **potential difference** across a component - great current through the component

Adding batteries in series - increases voltage and current

Adding batter in parallel - potentional difference and current stays tge same and each battery supplies less current.

## Resistance (P5)

Components - resist flow of charge.

Electric current flows through component - component heats up.

Greater resistance in a circuit - smaller current.

Adding resistors in series - increases total resistance.

Adding resistors in parallel - reduces total resistance and increases current through the battery.

Current-potential difference graphs - current through resistor is directly proportional to voltage across resistor.

Thermistor - resistance depends on temperature.

LDR - resistance depends on light intensity.

Resistance = potential difference / current

## Circuits and Electromagnetic Induction (P5)

In **series** circuits...

- current flowing through each component is the same
- potential difference across components add up to that across the battery
- potetional difference is
**largest**across components with**greatest**resistance.

In **parallel** circuits...

- current flowing through each component depends on resistance
- current running to and from battery is equal to sum of current running through each parallel component
- current is
**smallest**across components with**greatest**resistance

When a magnet is moved into a coil of wire, a **voltage** is induce. If ends of coil are connected, a **current** is induced. Moving the magnet out of the coil and moving the other pole of the magnet into the coil can induce the current in the opposite direction.

## Power and Energy (P5)

Power = measure of the rate of energy transfer.

**Power = potential difference x current**

Energy - measured in joules. Domestic energy is measure in kilowatt hours as joules are very small amounts of energy.

**Energy transferred = power x time**

Efficiency = the proportion of energy that is usefully transferred by an appliance.

**Efficiency (%) = energy usefully transferred / total energy supplied x 100**

## Waves (P6)

**Waves** = regular patterns of distrubance that transfer energy from one point to another. The two types are;

**Longitudal**(particles vibrate to and fro - side to side)**Transverse**(particles vibrate up and down)

**Amplitude** = maximum distrubance caused by wave (height).

**Wavelength** = distance between corresponding points on two adjacent disturbances.

**Frequency** = number of waves produced in one second. measured in hertz.

**Wave speed = frequency x wavelength**

## Behavoir of Waves (P6)

If a wave travels at a constant speed...

**increasing**frequency,**decreases**wavelength**decreasing**frequency,**increases**wavelength.

If a wave has a constant frequency...

**increasing**wave speed,**increases**wavelength**decreasing**wave speed,**decreases**wavelength.

**Refraction** = waves change direction when they pass between one medium to another.

**Diffraction** = waves spread out ferom the edges when they pass an obstacle or through a narrow gap.

**Reflection** = waves are reflected when a barrier is place in their path.

## Light and Interference (P6)

Light is reflected when it strikes a surface.

**Incident ray** = light travelling **towards** a surface.

**Reflected ray** = light travelling **away** from a surface.

Light...

- changes direction when it passes through one medium to another
- continues straight on when it meets a boundary at a right angle.

**Total internal reflection** = light is reflected when the angle of refraction is greater than 90 degrees as it can't escape from the medium.

**Constructive interference** = two waves arrive in step and reinforce each other.

**Destructive interference** = two waves arrive out of step and cancel each other out.

## Electromagnetic Radiation, Modulation and Signals

Electromagnetic radiations form the electromagnetic spectrum. **Visible spectrum** = the only part of the spectrum that can be seen.

Colours have..

- different frequencies
- different wave lengths

Photons = packets of energy. (intensity of a beam depends on the **amount** of **energy** carried by each photon)

Electromagnetic waves can travel through empty space but sound waves need a medium to travel through.

**Modulation** - makes a wave vary in amplitude or frequency.

**Analogue** signals = vary in exactly the way as information they carry (many different values).

**Digital** signals = uses two symbols (0 = off, 1 = on) which can be transmitted in a series of pulses.

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