P12/13: Waves

Question 1

what are transverse waves and eg.

Answer 1

• waves where points along its length vibrate 90 degrees to direction of energy transfer- travel in vacuum
• pass through SOLIDS ONLY
  e.g. ripples in water, s-waves, electromagnetic waves

Question 2

what are longitudinal waves and eg.

Answer 2

-waves where points along it length vibrate parallel to direction of energy transfer
-cant travel in vaccum
- PASS THROUGH SOLIDS/LIQUIDS
- e.g. sound waves
- P-waves
- pressure waves

Question 3

what is Amplitude , symbol and measured in?

Answer 3

-distance from undisturbed position to peak/trough of wave
symbol : A
measured in : metres

Question 4

what is wavelength , symbol and measured in?

Answer 4

distance from one point of wave to same point on next wave
symbol : lambda
measured in : metres

Question 5

what is frequency , symbol and measured in?

Answer 5

no. waves passing a point in a second
symbol : f
measured in : Hz

Question 6

what is time period , symbol and measured in?

Answer 6

time taken for single wave to pass a point
symbol : T
measured in : seconds

Question 7

equation for frequency and time period?

Answer 7

f= 1/T

Question 8

what is wave speed , symbol and measured in?

Answer 8

-distance travelled by a wave each second
symbol : V
measured in : M/S

Question 9

WAVE SPEED EQUN

Answer 9

wave speed = f x wave length

Question 10

laws of reflection

Answer 10

1. angle of incidence=angle of reflection
2. incidient ray,reflected ray and normal are all in the same plane

Question 11

what are the least, best surfaces for relfection

Answer 11

least reflective : ROUGH SURFACES
most reflective : FLAT SURFACES

Question 12

WHAT IS REFRACTION?

Answer 12

The change of direction in which they travelling when they cross the boundary between 1 medium to another

Question 13

what is REFLECTION, TRANSMISSION, ABSORBTION ?

Answer 13

REFLECTION: light will reflect if object is OPAQUE /not absorbed
- smoother the surface , stronger the reflective wave
TRANSMISSION: pass through transparant material
ABSORBTION: if frequ of light macthes energy levels of electrons - light will be absorbed by electrons and not REEMITTED

Question 14

how do soundwaves travel in the ear?

Answer 14

• travels down AUDITORY CANAL
• pressure of sound waves cause eardrum to VIBRATE
• small bones connected to this also vibrate and the vibrations transfer to fluid in INNER EAR —> nerve cells detect sound

Question 15

how does ultrasounds for medicine work?
and how does it image under surfaces?

Answer 15

measure the time between emmison and detection to show distance from source

• imaging under surfcaes is done becuase a crack causes WAVES TO REFLECT EARLIER than the rest, so will show up

Question 16

what is INFRASOUND?

Answer 16

sound wave that has a frequ below 20Hz: AKA seismic waves
types of seismic waves : P WAVES - long
S- WAVES - transverse

Question 17

groups of electromagnetic waves
(wavelength and frequency)

Answer 17

RADIO : 10^3 10^4
MICROWAVE: 10^-2 10^8
INFARED: 10^-5 10^12
VISIBLE: 10^-6 10^13
ULTRAVIOLET: 10^-8 10^15
X-RAY: 10^-10 10^17
GAMMA RAY: 10^-12 10^20

Question 18

for EM waves, as wavelength decreases…

shorter wavelength means smaller waves

Answer 18

frequency must INCREASE and energy of wave INCREASES

Question 19

how are radio waves produced?

Answer 19

produced by oscillations in electrical circuits
- when absorbed, create AC with same FREQUENCY AS RADIO WAVE

Question 20

hazards of UV, X-RAYS , GAMMA RAYS?

Answer 20

UV = skin ages prematurely ( skin cancer)
X-RAYS/GAMMA RAYS = ionsising radiation causing cancer /gene mutation

Question 21

uses of EM waves and why?

Answer 21

RADIO : tv, radio - LONG WAVELENGTH TRAVEL FAR WITHOUT LOSING QUALITY
MICROWAVES: satellites, cooking food - PENETRATE ATMOSPHERE TO REACH STAELLITES
INFRARED: cooking food/infrared cameras - TRANSFER THERMAL ENERGY
VISIBLE LIGHT: fibre optics - BEST REFLECTION/SCATTERING IN GLASS
UV : sun tanning, energy efficient lamps - RADIATES LEAST HEAT/MORE ENERGY
X-RAY: medical imaging and treatment /gamma - HIGH ENERGY, CAN PENETRATE MATERIAL EASILY

Question 22

what do soft tissue and bone do to xrays?

Answer 22

soft tissue: TRANSMITS
bone : ABSORBS

Question 23

why does refraction happen?

Answer 23

different mediums have different densities

Question 24

what happens when EM wave is absorbed?

Answer 24

• can be absorbed by an electron that gives it energy
• causes electron to move up energy level

Question 25

how is an EM emitted?

Answer 25

- if electron moves down energy level, it emits EM wave

Question 26

how are radio waves produced in the transmitting/recieving antenna?

Answer 26

**TRANSMITTING ANTENNA** : charge from AC oscillates up/down antenna ---> produces radio wave **RECIEVING ANTENNA**: metal aerial absorbs radio waves - creates AC with same frequnecy as transmitted wave

Question 27

what discoveries have seismic waves led to?

Answer 27

1. on opposite side of Earth to an earthquale **only P- WAVES are detected** suggesting : - *mantle is solid* (both types of waves pass) - *outer core is liquid* (only P waves pass) 2. refractions between layers **cause 2 shadow zones** (no p-waves detcted) suggesting: - inner core is solid --> due to size/positions of shadow zones

Question 28

required practical : extension

Answer 28

1. set up apparatus of a clamp stand and spring , without any masses on the spring 2. Align the marker to a value on the ruler, record this **initial length** of the spring 3. Add the **100 mass** hanger onto the spring 4. Record the **mass (in kg) and position (in cm**) from the ruler now that the spring has extended 5. **Add another 100 g** to the mass hanger 6. Record the new mass and position from the ruler now that the spring has extended further 7. Repeat this process until all masses have been added 8. The masses are then removed and **the entire process repeated again**, until it has been carried out a total of three times, and an average length is calculated

Question 29

force and acceleration

Answer 29

1. Use the metre ruler to **measure out intervals on the bench**, e.g. every 0.2 m for a total distance of 1 m. Draw straight lines with pencil or chalk across the table at these intervals 2. Attach the **bench pulley** to the end of the bench **Tie some string to the toy car** or trolley. Pass the string over the pulley and attach the mass hanger to the other end of the string 3. Make sure the **string is horizontal** (i.e. parallel to the bench) and is in line with the toy car or trolley 4. Hold the toy car or trolley at the start point **Attach the full set of weights** (total = 1.0 N) to the end of the string 5. **Release the toy car or trolley at the same time** as you or a partner starts the stopwatch. Press the stopwatch (in lap mode) at **each measured interval** on the bench and for the final time at 1.0 m 6. Record the results in the table and repeat step 5 to calculate an average time for each interval 7. Repeat steps 5-8 for **decreasing weights** on the weight hanger, e.g. 0.8 N, 0.6 N, 0.4 N, and 0.2 N. Make sure you place the masses that you remove from the weight stack onto the top of the car 8. Use the **distance between each interval** (0.2 m) and the **average time** it takes for the toy car or trolley to travel that distance to calculate the average speed per interval 9. Compare the **average speed between the first and last intervals for different weights** Use the equation below to calculate the acceleration

Question 30

INVESTIGATING wave properties

Answer 30

1. Set up a ripple tak with a screen underneath and fill the ripple tank with water to a depth of no more than 1 cm 2. Turn on the power supply and the light source to produce a wave pattern on the screen 3. The wavelength of the waves can be determined by measuring length of several waves and dividing this by no. waves 4. A stopwatch could be used - time for several waves to pass a point Frequency = number of waves/time 5. Record the frequency and wavelength in a table and repeat the measurements

Question 31

what property of waves doesnt change when moving from air to glass block and why?

Answer 31

frequency if speed and wavelength increase by same amount then frequency must stay constant