Physics topic 6 - Waves

Question 1

What is the definition of amplitude?

Answer 1

The maximum displacement of a point on a wave from it’s undisturbed position

Question 2

What is the definition of a wavelength?

Answer 2

The distance betweeen the same point on two adjacent waves.

Question 3

What is the defintion of frequency?

Answer 3

The amount of complete waves passing a fixed point per second

Question 4

What is the defintion of a period?

Answer 4

The amount of time taken for a single complete wave to pass a fixed point

Question 5

What is the formula for time period?

Answer 5

T = 1/f

Question 6

What is the defintion of a transverse wave?

Answer 6

A wave where the oscillations are perpendicular to the direction of energy transfer

Question 7

What are some exapmles of transverse waves?

Answer 7

. All EM waves
. Ripples and waves in water
. A wave on a string

Question 8

What is the defintion of a longitudanal wave?

Answer 8

A wave where the oscillations are parallel to the direction of energy transfer

Question 9

What are some examples of longitudanal waves?

Answer 9

. Sound waves i.e. ultrasound
. Shock waves like SOME seismic waves

Question 10

What are the 2 formulas for wave speed?

Answer 10

V = f * λ
V = s / t

Question 11

A radio wave has a frequency of 12 x 10⁶ Hz. Find it’s wavelength ( the speed of radio waves in air is 3 x 10⁸ )

Answer 11

λ = V / f
= (3 x 10⁸) / (12 x 10⁶) = 25 m

Question 12

A wave has a speed of 0.15m/s and a wavelength of 7.5 cm. Calculate it’s frequency.

Answer 12

f = V / λ
= 0.15 / 0.075 = 2 Hz

Question 13

Describe a suitable experiment to find the wavelength of a water wave?

Answer 13

• A signal generator connected to the ripple tank dipper produces waves at a known frequency.
• A lamp projects the wave crests as shadows onto a screen beneath the tank.
• The shadows must match the actual wave size to ensure accurate wavelength measurement.
• Each shadow line represents one wavelength of the water waves.
• Measure the distance across 10 wavelengths, either directly with a ruler or from a photo for greater accuracy.
• Use the equation v = f x λ, calculating wavelength by dividing the 10‑wavelength distance by 10.

Question 14

What are 2 ways that you could improve the ripple tank experiment?

Answer 14

. Viewing the waves in a dimly lit room, in order to see the shadows better
. Use a small amount of dish soap to reduce surface tension and reflection
. Fix ruler in place or use a set square ( TO REDUCE PARALLAX ERROR )

Question 15

How do you find the speed of a wave by using a string?

Answer 15

• Turn on the signal generator and vibration transducer. The string will start to vibrate
• Adjust the frequency of the signal generator until there’s a clear wave on the string. The frequency you need will depend on the length of string between the pulley and the transducer, and the masses that you’ve used
• Measure the wavelength of the waves by measuring multiple at once and then finding the average
• The frequency of the wave is whatever you set the signal generator to
• You can then find the wave speed

Question 16

What are 2 ways that you could improve the wave string experiment?

Answer 16

. Keep ruler fixed in place, or use a set square ( TO REDUCE PARALLAX ERROR )
. Keep constant tension on the string to reduce random error

Question 17

What are the 3 different ways that a wave can interact with another medium when coming into contact with it?

Answer 17

. Absorbtion
. Transmission
. Relfection

Question 18

What does it mean when a wave is absorbed?

Answer 18

The wave transfers it’s energy to the medium and as a result heats it up

Question 19

What does it mean when a wave is transmitted?

Answer 19

The wave carries on travelling through the new material, which may lead to refraction

Question 20

What does it mean when a wave is relected?

Answer 20

The wave bounces off of the medium at an angle, unless it is completely straight, and carries on moving

Question 21

What is the rule of reflection?

Answer 21

Angle of incidence = angle of relfection

Question 22

What is the angle of incidence?

Answer 22

The angle between the incoming ray and the normal

Question 23

What is the angle of reflection?

Answer 23

The angle between the reflected wave and the normal

Question 24

What is the normal?

Answer 24

The normal is an imaginary line that’s perpendicular to the surface at the point of incidence

Question 25

What are the 2 types of relection?

Answer 25

Specular or diffuse reflection

Question 26

What is specular reflection?

Answer 26

Reflection where the wave is reflected in a single direction by a smooth surface

Question 27

What is diffuse refelction?

Answer 27

Reflection where a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions

Question 28

What is an example of diffuse reflection?

Answer 28

Reflection off a piece of paper

Question 29

What is an example of specular reflection?

Answer 29

reflection off of a mirror

Question 30

Why does diffuse reflection happen?

Answer 30

Because the normal for each ray is at a different angle, so the angle of reflection will also be

Question 31

Name the type of reflection that happens when waves are reflected by a smooth mirror?

Answer 31

Specular reflection

Question 32

A light ray is incident on a mirror at an angle of 30 degrees. Draw a ray diagra to show it's reflection:

Answer 32

You should have: A straight line that represents the mirror, with dashed lines below it A dotted line at a 90 degree angle of the mirror (normal) A line with an arrow facing towards the mirror that comes into contact with the normal at an angle of 30 degrees Another line with an arrow, perpendicular to the first one, now facing away from the mirror

Question 33

What are all of the EM waves? (lowest freq to highest)

Answer 33

Radio waves Micro waves Infrared waves Visible light Ultra violet X-rays Gamma rays

Question 34

What is refraction?

Answer 34

When a wave crosses a boundary between materials, of differing densities, at an angle and changes direction

Question 35

What changes during refraction and what stays the same?

Answer 35

. Wavelength changes . Frequency stays the same

Question 36

How do you draw a ray diagram for a refracted ray?

Answer 36

.Start by drawing the boundary between the 2 materials and the normal .Draw an incident ray that meets the normal at the boundary (angle between ray and normal = angle of incidence) .Draw refracted ray on other side of the boundary . More optically dense = smaller than incidence . Less optically dense = larger than incidence

Question 37

Describe an experiment used to investigate refraction through transparent materials

Answer 37

- Place a transparent rectangular block on a piece of paper and trace around it. - Use a ray box or laser to shine a ray of light at the middle of one side of the block. - Trace the incident ray and mark where the light ray emerges on the opposite side of the block. - Remove the block and draw a straight line joining the incident ray to the emerging point to show the refracted ray through the block. - Draw the normal at the point where the light ray entered the block and use a protractor to measure the angle of incidence and the angle of refraction. - Repeat the experiment with rectangular blocks made from different materials, keeping the incident angle the same.

Question 38

Describe an experiment used to investigate how different materials reflect light by different amounts

Answer 38

- Take a piece of paper and draw a straight line across it. - Place an object so one of its sides lines up with this line. - Shine a ray of light at the object's surface and trace the incoming and reflected light beams. - Draw the normal at the point where the ray hits the object. Use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table. Also make a note of the width and brightness of the reflected light ray. - Repeat this experiment for a range of objects.

Question 39

Explain why a thin beam of light should be used for these experiments

Answer 39

So that the middle of the ray can be seen when tracing and measuring angles

Question 40

What are EM waves made up of?

Answer 40

Oscillating electric and magnetic fields

Question 41

How can radio waves used for communication? (i.e. radio broadcasting)

Answer 41

- electrons in the transmitter absorb sound waves, causing them to oscillate at a certain frequency - these oscillating electrons then produce an EM wave that carries the same frequency as the original sound - the EM wave leaves the transmitter and travels through the air towards the receiver - when the EM wave reaches the receiver, electrons in the receiver absorb the incoming wave - absorbing the EM wave makes the electrons in the receiver oscillate at the same frequency as the transmitter - this oscillation can then be converted back into sound or an electrical signal with the same frequency as the original wave

Question 42

How can radio waves be used for communication across long distances?

Answer 42

. Long wave radio waves can diffract around the curved surface of the earth, where it can be received in another location . Short wave radio waves reflect off of the ionosphere due to their low frequency . Very short wave radio waves must be in direct line of sight to the destination

Question 43

Why are signals between satellites transmitted as microwaves?

Answer 43

Because they have a high enough frequency to pass through the ionosphere

Question 44

How are microwaves used for communication?

Answer 44

. Transmitter sends microwave signal into space . Signal is picked up by satellite, then transmitted back to earth in a diff direction . Signal received by satellite dish back on earth

Question 45

How can microwaves be used to heat food?

Answer 45

. Microwaves are absorbed by the water molecules in food . This passes energy into them, causing them to heat up . They vibrate and transfer energy/heat to the other molecules in the food

Question 46

How do infrared cameras work?

Answer 46

. Camera detects infrared radiation and turns it into electrical signal . Signal then displayed on a screen . Hotter object is brighter on the screen

Question 47

How can IR waves be used for heating?

Answer 47

. Wire in electric heaters heats up with current . Wire emits IR radiation + visible light . IR waves absorbed by objects, heating them up . Energy is transferred to their thermal energy stores

Question 48

How can visible light be used for fibre optic?

Answer 48

. Light reflects through the fibre until it reaches the end . Light is not easily absorbed or scattered as it travels

Question 49

How can X - rays be used for medical imaging?

Answer 49

. X rays can easily pass through soft tissue, however is absorbed by denser material (bones). .Where the radiation is absorbed appears brighter on an image

Question 50

How can X rays and gamma rays be used for treating cancer?

Answer 50

. High doses of these rays can kill living cells . Waves are directed towards the cancer cells, constantly moving so to not harm healthy cells too much

Question 51

How can radiographers protect themselves against radiation?

Answer 51

. By wearing lead aprons . Standing behind a lead screen . Being in a separate room

Question 52

What are the dangers of all the waves?

Answer 52

Radio - none Micro - possible burns IR - possible burns Visible - impaired eyesight UV - premature aging, sunburn, blindness, skin cancer X rays - Ionisation (leads to cancer) Gamma - Ionisation (leads to cancer)

Question 53

What are the 2 types of lenses? What are their effects on passing rays of light?

Answer 53

Convex: makes rays converge Concave: makes rays diverge

Question 54

Where is the principal focus on convex and concave lenses?

Answer 54

Convex: Where rays parallel to the axis meet Concave: Where rays parallel to the axis appear to come from

Question 55

What are the 3 factors you describe an image by?

Answer 55

. Upright or inverted . Enlarged or diminished . Real of virtual

Question 56

How do you draw a ray diagram for a convex lens?

Answer 56

. Draw line from top of the object parallel to axis, going to lens . Draw line from top of object to middle of lens . Incident ray parallel to axis passes through focus . Ray passing through middle continues going straight . Where rays meet is top of image

Question 57

How do you draw a ray diagram for a concave lens?

Answer 57

. Draw line from top of the object parallel to axis, going to lens . Draw line from top of object to middle of lens . Refract parallel ray so that it joins with focus on object's side (make the part on the object's side dotted) . Ray passing through middle continues going straight . Where rays meet is top of image

Question 58

Can virtual images be projected onto a screen?

Answer 58

Fuh nah 💔🥀

Question 59

What is the formula for magnification?

Answer 59

Magnification = image height / object height

Question 60

What are sound waves caused by?

Answer 60

Vibrations

Question 61

Where do sound waves travel the furthest?

Answer 61

Solids, then liquids, then gases

Question 62

Can sound move in a vacuum?

Answer 62

Fuh nah 💔🥀, because there are no particles for it to pass onto

Question 63

How do we hear sound?

Answer 63

. Sound waves that reach the ear cause the ear drum to vibrate . Vibrations pass through tiny ear bones, to the cochlea . Cochlea turns vibrations into electrical signals, sent to brain

Question 64

What is the range of human hearing?

Answer 64

20 Hz - 20KHz

Question 65

What are ultrasound waves?

Answer 65

Sound waves above the range of human hearing (20KHz)

Question 66

What is partial reflection? How can this be used to measure distance?

Answer 66

When part of a wave (ultrasound) is refracted through a boundary, and another part of it gets reflected back. The time it takes for the wave to reach a detector can be used to measure the distance

Question 67

How can ultrasound be used to for pre-natal scanning?

Answer 67

. Ultrasound can pass through body, but is partially reflected at certain boundaries (fluid in the womb and skin of the foetus) . Timing and distribution of echoes can be processed into a video image by Comp.

Question 68

What are the differences between P and S waves?

Answer 68

P waves: Longitudanal, can pass through solid and liquid, faster than S waves S waves: Transverse, can't travel through fluids, slower than P waves

Question 69

How can P and S waves be used for exploring the Earth's structure?

Answer 69

.When seismic activity happens on one part of the Earth, P waves first travel through the Earth . They pass through the liquid outer core of the Earth and appear on the other side . A P wave blind spot is formed, because boundaries betweeen different parts of the Earth change the P wave's direction . After that, S waves are also sent out . However, they can't pass through the liquid outer core, so a much larger blind spot is also formed

Question 70

What is the relationship between emitting and absobring IR radiation (sorry I worded this one badly)

Answer 70

Emit > absorb = Object cooling down Absorb > emit = Object heating up Emit = absorb = Object at constant temp

Question 71

Describe the leslie cube experiment:

Answer 71

. Place the empty leslie cube onto the heatproof mat . Boil some water in the kettle and pour into the leslie cube . Use a ruler to check that the thermometer is a fixed distance away from the surface . From said distance, measure the temperature for the surface, waiting a few seconds for the reading to stabilise . Repeat for each side, at same distance

Question 72

What are some ways that you could improve the leslie cube experiment?

Answer 72

. Repeat measurements to calculate a mean . Refill cube with boiling water before each measurement . Insulate sides of the cube not being measured . Use digital infrared thermometer (if not already being used)