Waves And The EM Spectrum Flashcards
What happens towards the gamma rays end of spectrum
- more energy transferred
- short wavelength
- high frequency
What are the same for all electromagnetic waves
- are all transverse
- travel at the speed of light in a vacuum (3x10^8 m/s)
- travel at the same speed through the same material
How did Herschel make observations of the sun
Put a coloured filter over a telescope to try and make it safer
What did Herschel notice
Different coloured filters heat up by different amounts
What did Herschel do when he observed different coloured filters heat by different amounts, and what did he observe
He put a thermometer in the different colours by using a prism to break up the visible light. The temperature rose as as he moved from violet to red. He measured the temperature where there was no visible light at the red end of the spectrum
What did Herschel discover
Discovered that the temperature was highest at the red end of the spectrum. He discovered infrared (beyond red)
What did Ritter discover
He discovered ultraviolet when he tried to find invisible rays at the violet end of the spectrum
What did Ritter use and what did he see
He used silver chloride; which turns black when exposed to light. Happened fastest when exposed to invisible rays at the violet end
What is there towards the radio waves end of the spectrum
- less energy transferred
- long wavelength
- low frequency
What gives a tan but can cause cancer in cells
Ultraviolet
What is used to sterilise surgical instruments
Gamma rays
What is used to make toast
Infrared
What is used to change channels in a remote
Infrared
What is used to send information to and from satellites
Microwaves
How do microwaves heat food
The water molecules in the food absorb the microwave radiation and gain heat energy
What is reflection
The change in direction of a wave, at a boundary between materials, which does not enter the new material
What is the normal
A line perpendicular (at 90°) to the surface
What is the law of reflection
The angle of incidence is always equal to the angle of reflection
When a ray passes from air to glass
It slows down, as the refractive index of air is 1 and the refractive index of glass is 1.5
When Ray passes from glass to air
It speeds up, as it is going from a higher index to a lower
For entering a material with a higher refractive index
It refracts towards the normal
For entering a material with a lower refractive index
It refracts away from the normal
Diamond has a refractive index of 2.4 and water 1.3 what does this mean
The refractive index is a ratio that shows how much the material slows down the light. This shows that light travels faster in water than diamond
What is total internal reflection
It occurs when a wave no longer passes through the surface of a material it is inside. Instead, it is reflected
What is the critical angle
The certain angle that light is shone at for total internal reflection to occur
If an angle of incidence is less than the critical angle
It will result in refraction
If an angle of incidence is equal to the critical angle
No light leaves the material
If an angle of incidence is greater than the critical angle
It will result in reflection
What is fibre optic
Fibre optic cables use total internal reflection. Light and infrared radiation carries information down thin, solid plastic fibres
What is an endoscope
An endoscope is an instrument used medically. It has a bundle of very thin optical fibres which are used with lenses to see insides
How does the endoscope work
- the endoscope is put into the person
- light enters via the fibre optic cables
- it gets there by TIR
- the light is reflected off the person’s insides
- it returns by TIR
- a computer uses the reflected light to produce an image
When the waves go from deep water to shallow water
Wavelength decreases
Explain what happens to the direction of travel of waves when they go from deep water to shallow water
Due to refraction, the waves change direction and decrease in speed
What are the differences between longitudinal and transverse waves
Transverse waves are light waves. They are perpendicular to energy transfer. Longitudinal waves are sound waves and move upwards and downwards
What does a frequency of X Hz mean?
There are X numbers of cycles per second
Why are ultraviolet less harmful than xrays
They are both ionising, but xrays are more ionising.
