Topic 5 - Light and the Electromagnetic Spectrum Flashcards
SP5a - What two processes can be shown using a ray diagram?
- Reflection
- Refraction
SP5a - What do i and r represent in ray diagrams?
- i: Angle of incidence (between incident ray and the normal)
- r: Angle of reflection/refraction (between reflected/refracted ray and the normal)
SP5a - What is the relation between the angles of incidence and reflection/refraction?
i = r (Angle of incidence = angle of reflection/refraction)
This is the law of reflection
SP5a - What is the normal?
The line drawn perpendicular to the object light is reflecting off (or refracting through)
SP5a - Describe total internal reflection.
- TIR occurs when light refracts through a substance at sucha low angle of incidence that it doesn’t leave the other side
- This angle is called the critical
- If light enters at the critical, it will move along the interface
- If light enters at an angle smaller than the critical, it will cause TIR to happen
SP5a CP - Describe a method to explore refraction with varying angles of incidence,
- Place a ray box with a slit in front of it on a piece of paper
- Place a glass box the way of the ray of light thta is being produced
- Draw around the glass block
- Mark the point of entry and exit for the light aswell as two further points (such as origin and edge of paper) on the piece of paper
- Use your markings to draw lines representing the travel of the ray of light
- Repeat with ray box at different angles and compare your results
SP5b - What are the two types of reflection?
- Specular: When light is reflected evenly on a smooth surface
- Diffuse: When light is reflected in all directions on a rough surface
SP5b - Describe why a green object appears green in sunlight.
- Sunlight is made up of white light as it contains all the colours of the visible spectrum
- An object that appears green will reflect the green part of the spectrum but reflect all the other colours
SP5b - what effect would a blue filter have?
A blue filter would only transmit the blue part of the light that goes to it.
SP5d - What are the similarities between all EM waves?
- They are all transverse waves
- They all travel at (3x10^8m/s) ina vacuum
- They transfer energy
SP5d - How were infrared waves discovered?
- A prism was used to refract white light into the seven componenets.
- A thermometer was placed just outside of the red part of this spectrum.
- Another was placed in the spectrum.
- The thermometer next to red was warmer suggesting there was something warming it up
SP5e - List all the colours in the visible light spectrum.
ROYGBIV
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet
SP5e - List all of the EM waves in order of increasing wavelength/decreasing frequency.
- Gamma rays
- X-rays
- Ultraviolet
- Visible light
- Infrared
- Microwaves
- Radio waves
SP5e - Why do different telescopes need to be used to study different EM waves?
EM waves of different length get absorbed by different amounts by the atmosphere
SP5f - What can infrared be used for?
- Heating food
- Short range communication such as TV remotes
- Security systems
SP5f - What can microwaves be used for?
- Communications and satellite transmissions
- Heating up food and giving it energy
SP5f - What can radio waves be used for?
- Transmitting radio broadcasts
- Radio communications via satellites
SP5f - How are radio waves produced?
- Oscillations in electrical signals.
- Metal rods can be used as aerials because they can absorb and transmit these oscillations
SP5f - Whay can radio waves be used for longer ranges than microwaves?
- The way radio waves and microwaves travel is dependant on the angles they reach the ionosphere.
- At all angles, microwaves pass straight through and so there is maximum range they can be fired in a straight line.
- At some angles, radio waves are reflected by the ionosphere, becasue they have larger wavelengths.
- This means they don’t have to be fired directly to a point
SP5h - What are the uses of Ultraviolet rays?
- Disinfect waters by killing microorganisms
- Invisible ink due to fluoresence
- Security on bank notes
SP5h - What are the uses of x-rays?
Imaging of the inside of the body
SP5h - What are the uses of gamma radiation?
- Radiotherapy
- Sterilisation of medical equipment and food
- PET scanner
SP5i - What are the dangers of infrared radiation?
- Infrared radiation is absorbed by our body.
- We feel it as heat and an excess of it can destroy cells burning skin
SP5i - What are the dangers of ultraviolet light?
It can cause sunburn and damage to DNA which can lead to skin cancer
SP5i - What are the dangers of x-rays and gamma rays?
They can lead to mutations causing cancer.
SP5i - Why are UV x-rays and gamma rays dangerous?
- They are ionising radiation.
- They large amounts of energy due to high frequencies and short wavelengths which can pass through our skin.
SP5g - What is the difference between a hot and cold object in terms of radiation?
- All objects emit the same amount of radiation that they absorb.
- Hotter objects will emit more radiation than cold objects in the same time
SP5g - For the earth’s temperature to stay constant what must happen?
The amount of radiation it absorbs from the sun must be equal to the amount of radiation that the earth radiates into space
SP5g - Describe the greenhouse effect in terms of radiation.
- Energy from the sun is absorbed by the earth.
- The earth radiates this into the atmosphere
- Greenhouse gases in the atmosphere absorb this energy keeping it in the atmosphere
- This means that the earth doesn’t radiate into the atmosphere the same amount of energy it absorbed
- Thus the temperature of the earth rises
SP5g CP - Describe an experiment to explore how different surfaces absorb and emit infrared radiation using the following surfaces:
- Shiny black
- Shiny silver
- Dull black
- Dull grey
[Don’t worry guys its not just you I’m pretty sure we haven’t done this one]
- Pour water at 80° into four boiling tubes
- Cover each with one of the surfaces
- Put a thermometer in each
- Time it and record the temperautre at regular intervals
- The one that has the largest drop in temperature emits the most energy and thus must also absorb the most energy
- You would expect the results to be from largest to smallest change:
- Dull grey
- Dull black
- Shiny black
- Shiny silver
SP5c - What is a lens, and what is its power?
A lens is a small piece of transparent material made to refract light in a certain way
The power of a lens is how much it refracts light and is dependant on the shape and thickness of the lens
SP5c - What is the difference between a converging (convex) and diverging (concave) lens?
- Converging: Fatter in the middle and thinner at the top and bottom. Rays of light converge onto a focal point
- Diverging: Fatter at the top and bottom and thinner in the middle. Rays diverge away from each other once they pass through
SP5c - What does F mean on a ray diagram?
F is the focal length, i.e the length between the lens and its focal point
SP5c - When an object is placed more than 2F from a converging lens, what happens?
- Real image
- Inverted
- Less than 2F from other side of lens
- Smaller size
- (camera, eyes)
SP5c - When an object is placed at 2F from a converging lens, what happens?
- Real image
- Inverted
- 2F from other side of lens
- Same size
- (Photocopier)
SP5c - What happens when an object is placed between 2F and F from a converging lens?
- Real image
- Inverted
- More than 2F from other side of lens
- Larger size
- (Projector)
SP5c - What happens when an object is placed less than F from a converging lens?
- Virtual image
- Right way up
- Further than F on the same side of the lens
- Larger size
- (Magnifying glass, mirror)
SP5c - What happens when an object is placed more than F from a diverging lens?
- Virtual image
- Right way up
- Less than F on the same side
- Smaller size
SP5c - What is the difference between real and virtual images?
Real images:
- Can be projected onto a screen
- Same way round
- Appears on the opposite side of the lens
- Only produced by converging lenses
- e.g. Projectors
Virtual images:
- Can’t be projected onto a screen
- Inverted (left-to-right)
- Appears on the same side of the lens
- Produced by diverging and converging lenses depending on situation
- e.g. Mirrors
SP5c - What is the focal point of a lens?
The point where all the rays of light would converge onto and meet.
