Unit 2 Waves and the Electromagnetic Spectrum

Question 1

What is the function of waves and what do you need to produce a wave?

Answer 1

They carry energy from one place to another
A vibrating source

Question 2

Describe transverse waves

Answer 2

The particles in a transverse wave vibrate perpendicular to the direction in which the wave travels.

Question 3

Describe longitudinal waves

Answer 3

The particles in a longitudinal wave vibrate parallel to the direction in which the wave travels.

Question 4

What are compressions?

Answer 4

Places in the wave where the coils (or particles) are squashed together.

Question 5

What are refractions?

Answer 5

Places in the wave where the coils (or particles) are furthest apart.

Question 6

What is amplitude?

Answer 6

The maximum displacement of the wave from its undisturbed position.

Question 7

What is wavelength?

Answer 7

This is the distance between two consecutive crests (or troughs).
The distance between two consecutive compressions (or rarefactions).

Question 8

What is the period of a wave?

Answer 8

Time taken for one complete wave to pass a point.

Question 9

What is the frequency of a wave?

Answer 9

The number of waves passing a point in one second.

Question 10

What is the connection between frequency (f) and period (T)?

Answer 10

T = 1/f
f = 1/T

Question 11

What is the equation for wave speed?

Answer 11

wave speed = frequency (of wave) x wavelength (of wave)

Question 12

What is ultrasound?

Answer 12

-Sound which goes above the frequency of 20 000 Hz.
-Humans can no longer hear it.
-Ultrasound is a longitudinal sound wave.

Question 13

How is ultrasound used to scan the foetus in the womb?

Answer 13

By measuring the foetal head diameter an estimate can be made of the weight and age of the foetus.

Question 14

How is ultrasound used to detect flaws in metals?

Answer 14

-A probe sends an ultrasound wave into a test material. There are two indications, one from the initial pulse of the probe, and the second due to the back wall echo.
-A defect creates a third indication and simultaneously reduces the amplitude of the back wall indication.

Question 15

What are some of the uses of ultrasound in medicine?

Answer 15

-Ultrasound can be used to clean teeth. Dental hygienists use ultrasound.
-Focused pulses of ultrasound can break up kidney stones and gallstones into little fragments that can be passed from the body with less difficulty.
-Ultrasonic cleaners are used in hospitals to clean surgical instruments.

Question 16

What are some of the uses in industry?

Answer 16

-Ultrasound is used to determine how thick objects such as metals and plastic are.
-Bacteria, particularly those in sewage, can be killed by using ultrasonic waves.
-Ultrasonic waves can be used to weld plastic together. The waves make heat energy between the objects that are joined.

Question 17

What is sonar?

Answer 17

Sound, navigation and ranging. Sonar used sound waves to detect objects under water.
-A transmitter emits a pulse. This pulse travels to an object then bounces back again to a receiver. Upon hearing this echo, an operator can gather information about hazards in the water ahead, ocean depths, and other ship traffic. The pulses are emitted over a range of frequencies, from infrasonic to ultrasonic (ultrasonic sonar is highly accurate at short distances).

Question 18

What is radar?

Answer 18

Radar uses electromagnetic waves (microwaves) to detect aircraft and ships. As it travels at the speed of light it can detect fast moving objects. Radar stands for Radio Detection and Ranging; and it is used by air traffic control to guide aircraft to land, meteorologists to track storms/hurricanes and the military for surveillance or missile guidance systems.
-The radar transmitter sends out a pulse which is then reflected back by any object it hits. The transmitter then acts as a receiver and measures the time it takes for the reflection (echo) to arrive, and with that information can tell how far away the object is.

Question 19

What are the 7 types of waves in the electromagnetic spectrum (in decreasing wavelength and increasing frequency and energy)?

Answer 19

Radio waves - Micro waves - Infrared waves (IR) - Visible light - Ultra violet waves (UV) - X- rays - Gamma rays

Question 20

What are the properties of electromagnetic waves?

Answer 20

-they are transverse waves.
-they can travel through a vacuum.
-they travel at the same speed in vacuum i.e. the speed of light = 300 000 000 m/s.

Question 21

What are the main applications/uses and dangers of each of the electromagnetic waves?

Answer 21

GAMMA RAYS
Applications:
-treatment of cancerous tumours.
-sterilising medical equipment e.g. plastic syringes.
-detecting leaks in underground pipes.
-prolonging the shelf-life of fruit and veg.
Dangers:
-can disrupt the DNA in cells.
-can damage cells which may lead to cancer.
-can, in extreme cases, kill living cells.

X-RAYS
Application:
-medical diagnosis e.g. detecting fractures in bones.
-testing for metal fatigue.
Dangers:
-can kill/damage cells.
-can cause cancer.

UV
Applications:
-sun tanning.
-shows up security inks e.g. tickets, passports, banknotes.
-kills bacteria in water chillers
Dangers:
-can damage skin cells and lead to skin cancer.
-can affect the eyes e.g. conjunctivitis or cataracts.

VISIBLE LIGHT
Applications:
-human vision
-photography
-photosynthesis
Dangers:
-can damage eyes if too intense.

INFRARED RADIATION (IR):
Applications:
-night vision equipment
-TV remote controls
Dangers:
-as it is felt as heat it can cause skin burns

MICROWAVES
Applications:
-cooking food quickly
-radar waves for navigation
-mobile phone and satellite transmissions
Dangers:
-can cause internal bleeding of body tissues

RADIO WAVES
Applications:
-TV and radio signals
-Walkie talkies
Dangers:
-large doses are believed to cause cancer or leukaemia.
-some people have claimed that low frequency radio waves from overhead cables near their homes has affected their health.