TOPIC 6 - WAVES

What are the main stages in the coming life cycle of our Sun:

Main sequence; Red giant; White dwarf

Which statement is true for perfect black bodies?:

they are the best emitters of radiation

In a transverse wave, the direction of oscillation is _ to the direction of energy transfer by the wave:

perpendicular

‘The black-coloured flask will emit more infrared radiation than the silver-coloured flask during 10 minutes of cooling.’ 
Describe a method to test this hypothesis:

• heat water/ kettle

• add equal volume of hot water to each flask

• insert thermometer into each flask

• record initial temperature from both flask (or IR detector near each flask - dstnace between them should be the time - record initial reading)

• start stop clock + record the temps; after 10 minutes from both

• calculate the change in readings + compare results

When will the flasks emit infrared radiation at the greatest rate?:

in the beginning, within the first minute -> there is the greatest temperature difference between hot water + surroundings

Give three other similarities between radio waves and gamma rays:

• travel at the same speed in a vacuum/ air

• they can travel through a vacuum

• they are transverse

• they are electromagnetic waves

Give one medical use of gamma rays:

• medical imaging (PET scan, gamma camera, tracer)

• medical treatment (radiotherapy)

Explain why exposure to gamma rays can be harmful but exposure to radio waves is not harmful: 

gamma rays are weakly ionising; but radio waves are NOT ionising; so gamma can cause mutation in DNA that increase the risk of cancers

Explain how radio waves are produced at a specific frequency: 

radio waves are produced by oscilliations in electrical circuits; the radio waves have the same frequency as the oscillations

The microphone is used to convert the pressure variations in sound waves into variations in ___?:

current

What name is given to reflection from a smooth surface?:

specular reflection

What type of error mostly likely causes variation in results?:

random

Why has refraction not occurred when entering straight?:

all points on a wavefront enter the glass at the same time

Explain in terms of the wave fronts, why refraction happens at the boundary between air and glass:

different parts of the wavefront enter the glass at different times; the velocity of light is less in glass; so one part of the wave front changes speed before other parts

If an image is formed in front of the mirror/ lens - how do you describe it?:

virtual

Describe how the distance of the image from the lens decreases as the distance between the object and the lens increases:

increasing the object distance, decreases the image distance;  more rapidly at small distances/ more gradually at larger distances

Explain why the blue object appears black under a red filter:

only red light are transmitted by the filter; red is absorbed by the blue object; so no light is reflected by the blue object

how do you describe a wave passing through something?:

it is being transmitted

Give one use of ultraviolet:

energy efficient lamps; tan; kill microbes; detecting forged bank notes; security coding; attract insects

Describe the difference between transverse and longitudinal waves: 

• transverse waves; the oscillations are perpendicular to the direction of energy transfer

• in a longitudinal wave, the oscilattions are parallels to the direction of energy transfer

What is the advantage of repeating measurements and calculating a mean?:

reduces the effect of random errors

Explain how the teacher could determine the speed of the wave without measuring the wavelength:

measure the distance travelled by a wave with a metre ruler; measure the time taken with a stopwatch; distance/ time

Explain why using a wider ray would give less accurate results than using a narrower ray:

it is harder to judge where the centre of the ray is; causing a larger uncertainty in measurements

Describe a method the student could have used to obtain the results shown in the graph above (angle of incidence vs reflection):

• place a glass block on piece of paper

• draw around glass block

• use ray box to shine a ray of light through glass block

• mark the ray of light entering the block

• mark the ray of light emerging from the glass block

• join the points to show the path of the compelte ray through the block

• draw a normal line at 90 degrees to the surface

• use a protractor to measure both angles

• use a ray box to shine ray at diff angles of incidence

• increase the angle of incidence in 10 degree intervals

What property of the light wave changes when it is refracted?:

velocity

Describe what happens in the electrical circuit when the car aerial absorbs radio waves:

an alternating currect is induced in the electrical circuit; with the same frequency as the radio wave

Give two ways in which radio waves are different to sound waves:

radio waves are transverse; travel at a higher speed; don't need a medium; are electromagnetic

Explain why the car has a maximum speed:

there is a maximum forward force by motor; as speed of the car increases, air resistance increases; until air resistance is equal to the forward force in size; so the car can no longer accelerate

What is the function of a microphone?:

to convert pressure variations in sound waves into variations in current/pd

Explain how a moving-coil microphone works:

sound waves cause the diaphragm to vibrate; D causes the coil/ wire to vibrate; wire moves through the magnetic field/ cuts magentic field lines; a pd is induced

Explain how the properties of X-rays make them suitable for the medical imaging of bones:

passes through soft tissue; but absorbed by bone

How can the risk of boiling water be minimised?:

complete the investigation standing up

What is the Albedo value of a perfect black body?:

0.0

At night the air at point A (clear sky) cools faster than the air at point B (under cloud) - why?:

at night, more radiation is emitted from the Earth than absorbed from space; cloud reflects radiation towards Earth; at A, larger proportion of radiation will be emitted into space

What describes a scientific model?:

an idea use to explain observations and data

Why do scientists sometimes have different models like the wave and particle models of light?:

different models may be appropriate in different situations

Explain why scientists replace an old scientific model with a new model:

new evidence/ data; can't be explained with existing model/ old models show to be incorrect; new model explains new evidence (eg: nuclear model replaced ppm; bbt replaced others for creation of universe)

Explain why refraction happens at the boundary between the deep water and shallower water:

velocity is slower in shallow water; so edge of wave front entering shallow water slows down; but part of wave front in deeper water continues at higher speed; leading ot a change in direction of wave fronts

Explain why the wave fronts do not refract at the boundary when travelling straight in water:

every point on the wave front hits the shallow water at the same time; so every point slows down at the same time

Explain why the study of seismic waves provides evidence for the structure of the Earth’s core:

S-waves can't travel through a liquid; and don't travel through the outer core

Which EM wave has the higest frequency?:

gamma rays

What makes microwaves suitable for sending communications to a satellite in space?:

can travel through the atmosphere

What event leads to a neutron star forming?:

explosion of red super giant/ supernovae