Topic 5 - Light and the Electromagnetic Spectrum Flashcards
ray diagram
a way of modelling what happens when light is reflected or refracted
normal line
the line drawn at right angles to the barrier or mirror
law of reflection
when the angle of reflection is equal to the angle of incidence
refraction
When ray of light moves into a material and travels at a different speed, so it changes direction
total internal reflection
when light is completely reflected inside the glass
how do you see luminous objects
when light from the object enters you’re eyes
how do you see non-luminous objects
when the object reflects light
diffuse reflection
when the reflected light is scattered in all directions
specular reflection
when an object reflects the light evenly
what does ‘white light’ consist of
a mixture of different colours
how does a colour look white
it reflects all of the colours
filter
piece of transparent material that absorb some of the colours in the white light
how do we see colours (e.g. yellow)
all the colours are absorbed except yellow which is reflected
how do we see a blue colour using a blue filter?
a blue filter transmits (allows through) blue light and absorbed all the other colours
power of a lens
describes how much it bends light that passes through it
describe the shape of a converging lens
fatter in the middle than at the edges (oval)
what does a converging lens do to the rays of light
it makes parallel rays of light converge (come together) at the focal point
focal length
The distance between the focal point and the centre of the lens
describe the shape of a diverging lens
thinner in the middle, then at the edges
focal point
The point from which the rays seems to be coming after passing through the lens
How are real images formed?
When light rays come together
real image
an image that can be projected onto screen
when is a real image formed?
When an object is distant from a converging lens
If an object is distant from a converging lens? What does it produce?
produce a real image that is smaller than the object and also inverted (upside down)
Virtual image
An image that cannot be projected onto a screen
When will a converging lens produce a virtual image?
If the object is too close to the lens
What do divergent lens produce?
virtual images that are the same way up, much smaller and closer to the lens and the object
What colour do low frequencies produce?
red
What colours do high frequencies produce?
Blue
What do different frequencies of visible light produce?
Different colours
what type of wave are electromagnetic wave?
Transverse
What are the seven colours in the visible spectrum?
Red orange, yellow green blue indigo violet
what happens if the frequency of an electromagnetic wave is lower than that of red light?
Humans eyes cannot see it
Electromagnetic spectrum
The full range of electromagnetic waves
name the electromagnetic spectrum starting with the smallest frequency?
radio-waves, micro-waves, infrared, ultra violet, X-rays, gamma rays
what is visible light?
the part of the electromagnetic spectrum that detect
infrared radiation
A type of reading energy that is invisible to human eyes, but we can feel as heat
examples of infrared radiation
- Used for communication ranges such as between computer computers in the same room or from a TV to it remote control
- A grill or toaster transfers energy to food
- Security systems - they often have senses that can detect infrared radiation omitted by intruders
microwave examples
- Used for communications and satellite transmissions including mobile phones signals
- Used in a microwave oven - transfer energy to the food heating it up
Radio wave examples
used for transmitting radio broadcast and TV programmes
How a radio waves produced
by oscillations in an electrical circuits
what are oscillations
Variations in current voltage
how are radio waves transmitted?
- A metal rod wire can be used aerial to receive radio waves
- rasio waves are absorbed by the metal and cause oscillations in electrical circuit to connect to the aerial
what happens when radio waves reach the ionosphere?
if they reach the ionosphere at the right angle, they may be refracted enough to send them back towards the Earth
refraction
The bending of the path of wave of due to a change of velocity
ionosphere
region of charged particles in the atmosphere
what happens when microwaves reached the ionosphere?
They transmit through and are not refracted
how does the temperature of the earth stay the same?
It was right energy into space at the same average rate is absorbed
greenhouse effect
When some gas is in a atmosphere naturally absorb some energy keeping the air at a higher temperature than if there were an atmosphere
fluorescence
When some materials absorb ultralight radiation and remit it as a visible light
how do x-rays work
The race can pass through muscles and fat easily, but bone absorbs some x-rays
Gamma ray examples
- used to sterilise food and surgical instruments by killing potentially harmful microorganisms
- Used to kill cancer cells in radiotherapy
how does radio-therapy work
- A chemical that emits gamma rays is injected into the blood
- the chemical is designed to collect inside cancer cells
- a scanner outside the body then locates the cancer by finding the source of the gamma rays
microwave dangers
- Our bodies mostly water so the microwaves could heat cells from the inside
dangers of infrared radiation
Too much infrared radiation can damage or destroy cells causing bones to the skin
UV radiation dangers
- Can cause sunburn and damage DNA
- Too much exposure to ultraviolet radiation can lead to skin cancer
dangers of x-rays and gamma rays
- Can penetrate the body
- Excessive exposure to x-rays of gamma rays may cause mutations in DNA that can kill cells or cause cancer
how is electromagnetic radiation produced
By the changes in the electrons or the nuclear atoms
critical angle
The angle of incidence when the angle of refraction is 90°
-> angle of incidence for total internal reflection
Why is the satellite needed to give microwaves a similar range to radio wave?
because there is a maximum range for microwave communications because of the curved surface of the earth gets in the way
Why is the satellite needed to give microwaves a similar range to radio wave?
because there is a maximum range for microwave communications because of the curved surface of the earth gets in the way
how to wave lengths change the amount of radiation emitted by an object
The higher the temperature, the shorter the wavelength and higher temperatures mean more radiation emitted by an object
how does an system stay at constant temperature?
It must absorb the same power as it radiates
explain the greenhouse effect
greenhouse gases naturally absorb some energy in the atmosphere and this results in the Earth heating up due to the fact that the energy is being trapped and the Earth and atmosphere are radiating less power than they receive
uv radiation uses
- used to disinfect water by killing microorganisms in it
when is fluorescent ink visible?
When ultraviolet light shines on them
What happens to the body if a person has prolonged exposure to gamma rays
There is damage to the cells because gamma rays are ionising which causes cancer/mutations
Explain why the marks on a genuine bank note that cannot be seen using visible light CAN be seen when the UV radiation shines on the bank note
- UV energy is absorbed by electrons
- Electrons change shell (energy level) as UV makes electrons more ‘excited’ so they go up an electron shell
- When UV light is removed, electrons emit energy is visible light (move to lower electron shell)
- Process is called fluorescence
