Waves, Density and Pressure

Question 1

Equation for wave speed.

Answer 1

wave speed = frequency x wavelength
m/s Hz m

Question 2

Time period =

Answer 2

1 over frequency

Question 3

What is the frequency range of human hearing

Answer 3

20 - 20,000 Hz

Question 4

What is the main characteristic of waves

Answer 4

All waves transfer energy, but they do not transfer the particles of the medium
This means when a wave travels between two points, no matter actually travels with it, the points on the wave just vibrate back and forth about fixed positions

Question 5

Tip about how to accurately count wavefronts/ waves from birds eye view.

Answer 5

Count from 1 to the next, instead of counting each individual one.

Question 6

Describe an investigation to calculate the speed of sound.

Answer 6

Trundle Wheel- 100m between 2 people
One person will bang wooden blocks against each other
Second person has a stopwatch and starts it when they see the bang, stop it when they hear the sound,
Calculate speed with speed= distance over time

Question 7

What are the problems and how could you fix them with the investigation (speed of sound)

Answer 7

Measurement of time : Ensure to take repeat readings when timing intervals and calculate an average to keep this error to a minimum
Maximise the distance between the two people where possible. This will reduce the error in measurements of time because the time taken by the sound waves to travel will be greater

Question 8

Explain the problems with using a stopwatch.

Answer 8

For example, if a manual stopwatch is being used there could be variation in the time measured which can be up to 0.2 seconds due to a person’s reaction time
The time interval could be as little as 0.3 seconds for sound travelling in air
This means that the variation due to the stopwatch readings has a big influence on the results and they may not be reliable

Question 9

Use of Radio Waves

Answer 9

Communication and broadcasting (Radio and TV)

Question 10

Uses of microwaves

Answer 10

Satellite communication and cooking.

Question 11

Uses of infra-red waves

Answer 11

Remote controls
Thermal imaging (Medicine and Industry)
Electric Heaters
Heating or Cooking things
Night Vision equipment

Question 12

Uses of Visible light

Answer 12

Optical fibres
Photography

Question 13

Uses of Ultra-Violet

Answer 13

Fluorescent lighting
Tanning
Security marking (Detecting counterfeit money)

Question 14

Uses of X-rays

Answer 14

Imaging internal structures of the body and other objects.

Question 15

Uses of Gamma Rays

Answer 15

Used to sterilise medical equipment (gamma kills bacteria)
If aimed at cancerous tissue they can kill it

Question 16

How does wavelength affect the danger of Electromagnetic waves?

Answer 16

As wavelength becomes shorter, danger increases.

Question 17

Danger of Radio Waves.

Answer 17

None

Question 18

Dangers of Microwaves and how to prevent them.

Answer 18

Internal heating of body tissue

Question 19

Dangers of Infra-red and how to prevent them.

Answer 19

Skin-burns/ burning tissues and skin

Question 20

Dangers of Visible Light and how to prevent them.

Answer 20

Bright light can cause eye damage.

Question 21

Dangers of Ultra-Violet and how to prevent them.

Answer 21

Blindness - Good quality sunglasses absorb this light and prevent it from damaging the eye
Damage to surface cells/ skin damage - Sunscreen absorbs this light and prevents it from damaging the skin.

Question 22

Dangers of X-Rays and how to prevent them.

Answer 22

Long-term exposure can cause cancer - When used in medical industry level is low, Doctors leave room to avoid unnecessary exposure.
Cell mutation -

Question 23

Dangers of Gamma Rays and how to prevent them.

Answer 23

Cancer, gamma rays are ionising - People in contact with Gamma Rays are routinely tested for their radiation levels. badges are worn. Wear protective clothing and avoid contact with bare skin. Person is only exposed to low-levels.
Cell mutation -

Question 24

Density =
kg/m3

Answer 24

mass over volume
kg m3

Question 25

Pressure =
N/m2 or Pa

Answer 25

force over area
N m2

Question 26

Pressure difference =
n/m2

Answer 26

height x density x gravitational field strength
m kg/m3 N/kg

Question 27

What is the density of water?

Answer 27

1000 kg/m3
1 g/cm3

Question 28

1m3 in cm3 =

Answer 28

1,000,000 cm3

Question 29

1m2 in cm2 =

Answer 29

10,000 cm2

Question 30

Things to remember in questions involving different units.

Answer 30

1m3 does not equal 100cm3

Question 31

Examples of Transverse waves

Answer 31

Light, electromagnetic waves, Water Waves, S seismic waves

Question 32

Examples of Longitudinal Waves

Answer 32

Seismic P Waves
Sound Waves

Question 33

Describe the vibrations of Longitudinal waves.

Answer 33

Vibrations are parallel/ in the same direction that the wave travels/energy transfer.

Question 34

Describe the vibrations of Transverse waves.

Answer 34

Vibrations are 90o to the direction that the waves travel/energy transfer.

Question 35

What is oscillation?

Answer 35

Vibrations

Question 36

How to convert 48m^3 into cm^3.

Answer 36

48 x1,000,000 = 48000000

Question 37

How to convert 22,000 cm^3 into m^3.

Answer 37

22,000 divided by 1,000,000 = 0.022
1m^3 = 1 x 10^6 cm^3