P1 9-16

Question 1

What makes electromagnetic waves different from other waves?

Answer 1

They do not need a medium to travel through . They can travel though a vacuum, like space. Thai is how light and infrared waves reach the earth from the sun.

Question 2

Examples of electromagnetic waves?

Answer 2

Light, microwaves and X Ray’s

Question 3

State the electromagnetic spectrum from least to most energy

Answer 3

Radio waves 
Microwaves
Infrared 
Visible light 
Ultraviolet 
X rays 
Gamma rays

Question 4

How does frequency , wavelength and amount of energy relate?

Answer 4

The more the energy, the more the frequency, but the shorter the wavelengths.

Question 5

What is the law of reflection?

Answer 5

The angle of incidence is always equal to the angle of reflection

Question 6

What is refraction?

Answer 6

When waves go from one medium to another they can be refracted. As they enter a different medium their speed changes and this causes them to change their direction. If the wave slows down it bends towards the normal, if it speeds up it bends away from the normal.

Question 7

What is diffraction?

Answer 7

Whenever the waves pass through a gap or move around an obstacle, they spread out.

Question 8

How does the wavelength and size of the gap affect diffraction?

Answer 8

In general, the longer the wavelength or the smaller the gap, the greater the diffraction. The strongest diffraction occurs when the gap is the same size as the wavelength.

Question 9

What problems can diffraction cause?

Answer 9

Diffraction causes problems when using optical instruments like microscopes and telescopes. When light enters the instrument, it passes through a small gap and diffracts a little. This can lead to a blurry image or a loss of detail.

Question 10

What is total internal reflection?

Answer 10

If the light hits the boundary between the glass and air at a big enough angle of incidence, all of the light stays within the glass; it is all reflected internally. It happens if the angle is above the critical angle for the material.

Question 11

When can total internal reflection be seen?

Answer 11

When light travels from a dense object to a less dense one. E.g water to air, glass to air, Perspex to air

Question 12

What are the requirements for total internal reflection to happen?

Answer 12

• The angle of the light is greater than the critical angle.
• The light is travelling in the denser of the two materials.

Question 13

What are optical fibres? What do they do?

Answer 13

very fine glass cables. They can be used to transmit large amounts of information or to help doctors peer inside the body without cutting their patient open.

Question 14

How do waves pass along optical fibres?

Answer 14

Waves travel along optical fibres by Total Internal Reflection. They enter the fibre and hit the edge at an angle greater than the critical angle. They reflect off the inside of the glass fibre until they reach the other end.

Question 15

How does fibre optic broadband work?

Answer 15

With fibre optic broadband, pulses of visible light or infrared are sent down optical bres. This allows large amounts of data to be sent very quickly. Fibre optic broadband is generally much faster than using normal phone lines.

Question 16

How do endoscopes work?

Answer 16

a medical instrument that can produce an image of the inside of the body through a tiny incision rather than cutting the patient open. Inside the endoscope there are several bundles of optic fibres. The endoscope is inserted into the body and visible light is sent down one of the bundles of cables. The light illuminates the inside of the body and is then reflected back down a separate bundle of fibres. The doctor either looks along the fibre or the image is sent to a TV screen, providing a clear picture of the patient’s insides.

Question 17

What makes lasers different from normal light?

Answer 17

It is just one colour - usually red. It produces a narrow beam of light, and does not spread out a lot as it travels.

Question 18

Uses of lasers?

Answer 18

• surgery and dental treatments
• guiding weapons
• CD, DVD, and Blu-ray players
• cutting materials such as steel plates.

Question 19

Describe the waves emitted from a laser

Answer 19

The waves all have the same frequency and they are in sync with each other. All the crests and troughs line up. We say that the light is in phase. Because of these features, lasers are described as a source of coherent monochromatic light. The laser light beam does not spread out very much. It is described as having a low divergence.

Question 20

How do lasers read CDs and DVDs ?

Answer 20

On a CD the information on the disc is stored on the shiny side as a series of pits. This digital information is read by a laser. As the disc spins, a laser reflects from its surface. When the light enters a pit there is no reflection, and so the detector reads a series of light pulses. This code is then converted into sounds or images by computer chips in the CD player.

Question 21

How do microwaves cook food?

Answer 21

A microwave oven produces a steady stream of microwaves. Instead of just heating the surface of the food being cooked, they travel about 1 cm into the food. The microwaves are absorbed by fat and water inside the food. This causes the food to heat up. Inside the oven there are shiny metal surfaces. These surfaces reflect the microwaves so that all parts of the food are heated. This helps to make sure the food is fully cooked.

Question 22

How is energy transferred when cooking food?

Answer 22

In both infrared and microwave cooking, energy is transferred from the electromagnetic wave to the molecules inside or on the food. This energy is then transferred to the rest of the food through conduction and convection. In microwave ovens, the fat and water molecules inside the outer layers of the food gain kinetic energy as they absorb the microwaves. In the case of infrared, only the particles on the surface of the food gain kinetic energy as they absorb the infrared waves.

Question 23

How do phones work?

Answer 23

All types of mobile phone send and receive microwaves. When you talk your phone converts the sound into a microwave signal which it sends to the nearest phone mast. there needs to be a line of sight between the phone and receiver.

Question 24

What can stop a microwave going from the transmitter to the reciever?

Answer 24

there needs to be a line of sight between the phone and receiver. Microwaves travel in straight lines,

• but in some areas hills and buildings get in the way
• poor weather conditions
• large surfaces of water
• curvature of the Earth gets in the way.

Question 25

How can you reduce signal loss when phoning?

Answer 25

microwave transmitters are usually placed close together to ensure the signal received remains strong. They are also placed high on hills to avoid other obstructions.

Question 26

What is the difference between analogue and digital?

Answer 26

• Digital signals can only have two values. The signal is either on or off; it is a series of pulses. These two states are often represented by numbers: on is 1 and off is 0.

An analogue signal is one which continuously changes its values. An analogue signal is always changing through different values.