Waves And Magnets Flashcards
What is the range a human ear can detect sound?
Detect sound in the range of about 20Hz to 20000Hz
What happens when a wave passes from one medium into another?
It can be refracted and change direction
What does refracted mean?
Where a wave meets a boundary between 2 different materials and changes direction
What is a medium?
An object or substance
What does the direction of refraction depend on?
♡Angle at which the wave hits the boundary
♡The materials involved
For light rays, the way in which a material affects refraction is called…?
The refractive index (measure of the extent to which light is refracted by a material)
Define refractive index?
Measure of the extent to which light is refracted by a material
What happens when light passes from air into glass?
The velocity of light decreases (slows down) causing the direction of the waves to change
When waves slow down (usually when entering the object) what happens to the wave?
It bends towards the normal (right angle) and pass through the block
What happens to waves when they pass from the glass block back to the air?
Their velocity (speed) increases and bends away from the normal, making the object appear to have shifted position
If a wave enters or leaves the object/medium at right angles to the surface (along the normal) what happens to the waves direction?
It doesn’t change direction
When a wave slows down, is it refracted towards or away from the normal?
TOWARDS THE NORMAL
When a wave speeds up, is it refracted away or towards the normal?
Refracted away from the normal
What type of wave are electromagnetic waves (EM)?
Transverse
What is the same for all the EM waves?
All travel at the same velocity (speed of light) in air or in a vacuum
What do the two ends of the EM spectrum show?
EM spectrum extends from low frequency and low energy waves to high frequency and high energy waves
What light can human eyes detect?
Only capable of detecting visible light
The human eye can only detect visible light, what does this mean in terms of detecting EM waves?
Human eye can only detect a very limited range of EM waves
How many types of EM waves are there?
7 types:
●Radio waves
●Microwaves
●Infared waves
●Visible light
●Ultraviolet waves
●X-rays
●Gamma rays
What happens when we pass white light through a prism?
Splits into a spectrum (seven colours of the rainbow 🌈 )
Starting with red all the way to violet, what is the frequency and wavelength of each end?
Red end of spectrum=lower frequency,longer wavelength
Violet end of spectrum=higher frequency, shorter wavelength
What does each colour of light have?
Different frequency and wavelength
What is the sentencd to remember the electromagnetic spectrum?
Raw Meat Is Very Unsanitary eXcept Giraffe
The EM spectrum starts from radio waves to gamma rays at the end, what happens to the frequency and wavelength?
●Frequency increases from radio waves to gamma rays
●Wavelength decreases from radio waves to gamma rays
What do scientists say about the electromagnetic spectrum?
It is a continous spectrum
Scientists call the electromagnetic spectrum a continous spectrum, what does this mean?
The cut-off point between one type of a wave and another is not always clear
All electromagnetic waves travel at the same speed in a vacuum, what is the speed?
300 million / 3x10^8 m/s
(Meteres per second)
Where are radiowaves used?
Television, radio, bluetooth
Where are microwaves used?
Satellite communications and to cook food
What are the uses of infrared?
Electrical heaters, cooking food, infrared heaters
Where is visible light used?
Fibre optic communications
Where is ultraviolet waves (UV) used?
Energy efficient light bulbs and sunbeds
Uses of x-rays?
Medical imaging and treatment
Gamma ray uses?
Tumour treatment and sterilising food
What does changes in atoms and in the nucleus of atoms cause?
Can result in EM waves being generated or absorbed
What does the risk of damage from EM waves depend on?
Risk of damage from EM waves depends on TYPE OF RADIATION AND AMOUNT OF EXPOSURE
Give an example of where changes in atoms causes EM waves to be generated?
●Electrins moving between energy levels as a result of heat or electrical excitation generates waves such as infrared waves, visible light, UV waves, X-Rays
What do ultraviolet waves, x-rays and gamma rays do to the body?
If they carry enough energy they can have a hazardous effect on the human body
How do UV waves damage the bod?
UV waves cause skin to age prematurely and increase the risk of cancer
How do x-rays and gamma rays damage the body?
X-rays and gamma rays are ionising radiation, damage cells by ionising atoms if absorbed by nucleus of cell it can cause gene mutations and cancer
How does a lens form an image?
By reflecting light
What are the two types of lens?
●Convex
●Concave
Describe the shape of a convex lens?
Wider in middle than at edges
What happens to parallel rays of light when it enters a convex lens?
Parallel rays of light are brought to thr focal point/principal focus (point where parallel rays of light travelling through a lens meet)
What is the other name given to cover lenses?
As parallel rays of light entering a convex lens converge (come together) they are sometimes called converging lenses
What is the name given to the distance from the lens to the principal focus/focal point?
The focal length
Describe the shape of a concave lens?
Wider at edges than in the middle
What happens to parallel rays of light entering a concave lens?
They are spread out
When parallel rays of light enter a concave lens it spreads out, what does this make the rays appear to be coming from?
The principal focus on the same side of the lens that they originated
What are concave lenses also called?
Diverging lenses as when light enters a concave lens it diverges (spreads out)
What type of images do convex lenses produce?
Produce real or virtual images
What type of images do concave lenses create?
Virtual image
What is a real image?
Opposite side of lens to object, can be projected onto a screen
What is a virtual image?
Same side as object, only seen by looking through lens
What are the key features of an object that has gone through a convex lens further than 2 focal points (2F)?
•image is smaller than object (diminished)
•image is inverted
•real image - rays meet at a point
What are the properties of an image that had gone through a convex lens less than 2 focal point lengths away?
•Image larger than object
•Inverted
•Real image
What is the object in a lens diagram?
Object is the thing that will appear different when it’s passed through the lens
What is the image in a lens object?
The thing that is produced once passed through the lens
Why does magnification have no units?
Because it’s z ratio
What type of image is produced in a convex lens when the object is less than 1 focal length from the lens?
Magnified image
What are the 3 key features of a convex lens,less than 1 focal length away from thd lens?
•Image is magnified
•Same way up
•Virtual (image not real as don’t actually meet at a point)
When is the only time a convex lens produces a virtual image?
When it’s used as a magnifying glass
What is ‘visible light’?
Electromagnetic waves that can be detected by the human eye
What happens when light is incident on (arrives and hits)?
An object can be reflected, absorbed or trsansmitted
What is specular reflection?
When an object is reflected by a smooth surface in a single direction (a mirror)
What type of reflection is this…
Reflection by a smooth surface in a single direction?
Specular reflection
Give an object that uses specular reflection?
A mirror
What is diffuse reflection?
Reflection from a rough surface where light is scattered
What type of reflection is this…
Reflection from a rough surface where the light is scattered?
Diffuse reflection
What does transparent mean in terms of light?
Light rays transmit coherently (don’t get jumbled up) so objects on other side can be seen clearly
What does a transparent object do to light rays?
Transmits light coherently (light rays don’t get jumbled up) so objects on other side can be seen clearly
Is the object through something transparent clear or clouded?
Clear
What does a translucent object do to light rays?
Scatters the light rays
What sort of image does a translucent object create?
An image which you can’t see clearly
Does a translucent object transmit light?
Yes, but rays are scattered so objects can’t be seen clearly through them
What does an opaque object do to light rays?
Reflects or absorbs all light incident (light that hits a surface) so no light passes through them
How much light passes through an opaque object?
None
Define the word light incident?
Light that hits a surface
What happens when the colour of the colour filter is the same colour as the object?
Object appears it’s true colour
What colour does a red or blue striped object appear through a red filter?
Red and black as filter only allows red light through
A red filter shows the colours of an object to be red and black, what actual colours are the object?
Red or blue stripped
What happens to the colour of red or blue stripped objects when they pass through a green filter?
Appear black, green filter doesn’t allow red or blue to pass through
An object appears black through green filter paper, what is the actual colour of the object?
Red or blue stripped
What are bodies in physics?
Objects
Do all bodies(objects) emit and absorb infrared radiation?
Yes
What does the rate an object emit radiation depend on?
Surface of object and the temp
How fast does a hot body (object) emit radiation?
Hotter the body, faster it emits infrared radiation
What does a perfect black body do?
°absorbs all infrared radiation incident on it
°doesn’t transmit or reflect any infrared radiation
What sort of body absorbs all infrared radiation incident on it?
Perfect black body
What sort of body doesn’t reflect ot transmit any infrared radiation?
Perfect black body
How does a colour filter work?
Filters(blocks) out some colours while letting othdr through
Does a colour filter produce a colour effect when viewing coloured objects?
NO - this is a common mistake made !!!
What does the temperature of a body (object) determine?
The Rate it emits radiation
The wavelength of the radiation
What happens to radiation when temperature of a black body increases?
As temp increases the amount of radiation an object emits (at all wavelengths) increases
Does the radiation intensity of a shorter wavelength increase slower of faster than a longer wavelength?
Faster
What does the temperature of an object depend on?
The balance between the radiation absorbed and emitted
Why does the ground on a sunny day increase in temperature?
Grounds absorbs radiation from the sun faster than it emits, as ground gets warmer the rate which the ground emits will increase
Why is the ground a constant temperature on a sunny day?
Eventually the rate of emission is equal to the rate of absorption of the ground
What does the temperature of earth depend on? (Black bodies)
▪︎How much energy recieved from sun
▪︎How much energy emitted into space
▪︎How much energy is reflected back into space
Does the temperature of earth depend on how much energy is emitted into space?
Yes
Does the temp of the earth depend on how much energy is recieved by the sun?
Yes
Does the temperature of the earth depend on how much energy is reflected back into space?
Yes
What does the earths atmosphere affect? *radiation
How much radiation is emitted from the surface escapes into space
How much of the radiation thats emitted and escapes into space is affected by what?
Earth’s atmosphere
The coals in a barbecue glow red, burning magnesium is bright white, what does this show about temp?
Magnesium burns at a higher temp
What are Matt black surfaces best emitters and absorbers of?
Infrared radiation
What type of surfaces absorbs and emits infrared radiation thd best?
Matt black surfaces
Does a cooler or hotter object emit more radiation in a give time?
Hotter object
Ad an object gets hotter what type of wavelength radiation does it emit?
Shorter wavelength radiation than cooler objects
What wavelength does a very hot object emit?
Shorter wavelength radition
Why do very hot objects produce visible light?
Very hot objects emit shorter wavelength radiation
Very hot objects emit shorter wavelength radiation, what does this result in?
Visible light
Is a good emmiter a good black body?
Yes
If an object is cooler than its surroundings, what will happen to its temp?
It will absorb more radiation than it emits so object temp will increase
What does an object at constant temp mean is happening interms of absorbing and emitting radiation ?
Object is absorbing radiation at the same rate it is emitting
What does is the temp an object when its absorbing radiation at the same rare it is emitting?
Constant temp
If an object is warmer than its surroundings What will happen to its temp?
Decrease as it will emit more than absorbs
If the temp of an object decreases what is the temp of the surroundings?
Cooler than object
If an object is warmer than its surroundings will it emit more or less radiation?
More
Why are cloudy nights warmer than cloudless nights?
Clouds reflect infrared back to earth to prevent it being radiated into space
Infrared emission from most to lowest?
Matt black
Shiny black
White
Shiny metallic
What happens to infrared when it hits a Shiny metallic surface?
Tends to be reflected
What material is the best emitter and absorber of infrared?
Matt black surfaces
What are the two types of poles?
North and south
What is the attraction between the poles?
☆Like poles repel
☆Unlike poles attract
Where is the force the strongest on a magnet?
At the poles
Define magnetic field?
Region around a magnet where a force acts on another magnet
What does the magnetic fields strength depend on?
Srength depends on distance from magnet
What are the two types of magnets that produce a magnetic field?
Permanent magnet
Induced magnet
What is a permanent magnet?
Produces its own magnetic field
What is an induced magnet?
Becomes a magnet when placed in a magnetic field
What happens to induced magnets when they are removed from their magnetic field?
They lose their magnetism very quickly
What is density of field lines called?
Flux density
What does flux density show?
Strength of magnetic field at that point
If magnetic lines are closer what does this mean?
The closer the lines the higher the flux density
What does a high flux density mean?
The higher the flux density the stronger the field and the greater the force the other magnet would feel
What is a magnetic compass?
Contains a small bar magnetic and has a compass needle that aligns with the earth’s magnetic field
What does a magnetic compass provide evidence of?
That the earth’s core is magnetic
What do we use magnetic compasses to plot?
The field around a magnet
What are the first 3 steps to plot the field around a magnetic bar?
1-place the bar magnet on paper
2-place compass at one end of magnet
3-on the paper mark where the point of the needle compass is
What are the last 3 stages of plotting the field around a bar magnet?
4-move the compass so the tail if the needle is at the point you just marked
5-mark the new point
6-repeat until full field is plotted
What happens when a current flows in a conducting wire?
A magnetic field is produced around the wire
What do the direction of field lines depend on?
Direction of current, can be found using the right hand grip method
What is the right hand grip method?
☆Grip the wire with your right hand, thumb points in direction of current
☆Fingers curled around wire show the direction of the field lines
How do we know the direction of the current using the right hand grip method?
The thumb points in the direction of the current
How do we know the direction of the magnetic field using the right hand grip method?
Fingers curled around the wire point to the direction of magnetic field
What does the strength of a magnetic field depend on?
Depends on size of thd current and distance from wire
When is a solenoid formed?
When a wire is looped into a cyndrical coil
What does shaping wire into a solenoid do?
Increases the magnetic field strength
What increases the solenoid magnetic field even more?
When an iron core is added, creates an electromagnet
What does a solenoid convert electrical energy into?
Mechanical energy
How does a solenoid increase the magnetic field?
•Concentrates longer piece of wire into a small area
•Looped shape means magnetic field lines are all in the same direction
How can the north pole of a solenoid be found?
By using the right hand grip method
How do the right hand grip method show the current of a solenoid?
~Hold solenoid in right hand, fingers will follow the direction of current
How does the right hand grip method show the north pole of a solenoid?
Thumb points to the direction of the north pole when holding it
Many devices use electromagnets, what is an electromagnet?
A magnet consisting of an iron or steel core wound with a coil of wire, through which a current is passed
How does an electric bell work (electromagnetic device)?
1~switch is pushed,electromagnet is magnetised
2~electromagnetic attracts the armature
3~hammer strikes the gong and breaks the circuit
4~armature springs back,completing the circuit again and remagnestising the electromagnet
How do we use a compass to detect a current?
Current is off, compass needle lines up with the earth’s magnetic field. Current on the compass needle deflects=shows there is a magnetic field
What does it mean if the compass needle deflects when using it to detect a current?
Current is on so there is a magnetic field
When we turn on the current of a solenoid, what sort of magnetic field is produced?
A strong and uniform magnetic field is produced inside the solenoid
Why are electromagnets very useful?
As we can change the strength of the magnetic field by changing the current and we can turn it on or off
What are the 3 ways you can increase the strength of the magnetic field produced by a solenoid?
▪︎Increase size of current
▪︎Number of coil turns
▪︎Iron core
