Physics P1: Electromagnetic Waves

On average, what length are radio waves?

Radio waves are about 1km long.

What are radio waves used for?

Radio waves are used for TV, radio, mobile phone calls & bluetooth.

What was created in The Big Bang?

Space, time & matter.

What is the Big Bang Theory?

The Big Bang Theory states the universe started with a massive explosion from a central point.

Given that electromagnetic waves travel at 300 million m/s, what is the wavelength of waves travelling at 200 million Hz?

Wavelength = Wavespeed ÷ Frequency = 300 million m/s ÷ 200 million hz = 1.5 m

Which electromagnetic waves are the shortest?

X-rays and gamma rays.

Name the different aspects of the electromagnetic spectrum.

X-rays, gamma rays, UV, visible light, IR, microwaves, radio waves.

A distant star explodes and emits both light rays and gamma rays. Why do both type of rays arrive at Earth at the same time?

All aspects of the electromagnetic spectrum travel at the same speed, 300 million m/s.

How do we know the galaxies are moving away from us?

All the distant galaxies show a red-shift, meaning they are moving away from us.

What evidence is there to support The Big Bang Theory?

Cosmic micro wave background radiation proves there must have been a very large explosion in the past.

Who discovered red-shift?

Edwin Hubble discovered red shift.

If the galaxies are speeding up in expansion, what would be the future of the universe?

Galaxies will expand forever everything will die out in a big yawn.

If the galaxies were slowing down in expansion, what would be the future of the universe?

Galaxies will reverse and go into a big crunch.

Galaxy X is 200 million light years away whilst Galaxy Y is 350 million light years away. Which galaxy has the largest red-shift?

Galaxy Y.

How do optical fibres transport information?

IR or light is fed into optical fibres. When it touches the surface of the cable, it is reflected back into the cable.

Why are optical fibre signals more secure than radio waves?

Optical fibre signals cannot be interpreted by others as the signals stay within the cable whereas radio waves are exposed in air.

What type of electromagnetic radiation do the following emit: 1. TV transmitter 2. Satellite TV Transmitter 3. Remote Control 4. TV Receiver

1. Radio waves. 2. Microwaves. 3. Infrared. 4. Light waves.

At what speed do all electromagnetic waves travel?

300 million m/s

What are the practical applications of Infrared waves?

1. *Optical Fibres* use IR to transmit information because IR is absorbed less by fibres than light, therefore retaining as much information as possible. 2. *Remote Controls* send IR to TV sets. 3. *Infrared Cameras* are used to detect people and animals in darkness.

Why do astronomers think the expansion of the universe is accelerating?

It is believed there is an attractive force called 'dark energy'. It is causing attraction and accelerating expansion.

What will happen to microwave background radiation as the universe continues to expand?

It will spread even further and transfer into longer radiation forms like radio waves.

What is white light?

Light from ordinary lights and the sun is known as white light.

How does a digital camera produce photographs?

Light is focused by a lens onto a sensor consisting of lift sensitive cells. Each pixel provides a dot of colour for the image. This image is stored on an electronic memory card.

How does a film camera operate?

Light is focused by a lens onto light sensitive film. This film must be developed to see the image.

What effect does blue-shift have on wavelength?

Light waves are squashed together, shifting towards the blue aspect of the spectrum.

Why can light waves and IR in optical fibres carry more information than radio waves?

Light waves have a shorter wavelength and therefore have larger amplitudes. Thus, they contain more energy.

Why are micro waves used for satellite TV whilst radio waves are used for terrestrial TV?

Micro waves are powerful enough to penetrate the atmosphere and reach satellites whereas radio waves are less powerful but only need to communicate with sea-level masts. Also, radio waves can spread out much more easily and cover a vast area.

What are the applications of microwaves?

Micro waves are used for communications: satellite phones, satellite TV, mobile phone signals.

Why are microwaves used for mobile phone signals?

Micro waves don't spread out as much as radio waves and are therefore more precise when sending messages to specific areas.

What effect does red-shift have on wavelength?

Red-shift forces light waves to stretch out and shift towards the red aspect of the spectrum.

What is meant by 'red-shift of a light source'?

Red-shift is when light shifts to longer wavelengths because the light source is moving away from us.

Why are short-wavelength radio waves used for TV?

Short-length radio waves can transmit more information than long-length radio waves.

Why are microwaves used for satellite TV and phones?

The waves can travel between satellites and Earth and they don't spread out as much as radio waves and therefore don't weaken in intensity.

Why do microwaves spread out less than radio waves?

They have a shorter wavelength.

Why do we think the universe is expanding?

We think the universe is expanding because the distant galaxies are moving away from us. This means they must have expanded from the centre of the universe.