Section 18 - Waves and the electromagnetic spectrum - EM waves and uses Flashcards
What are the speed of EM waves like in a vacuum and in different materials?
All travel at same speed in vacuum but at different speeds in different materials
Order of EM spectrum from longest wavelength/lowest frequency to shortest wavelength/highest frequency?
Radio waves => Microwaves => Infrared => Visible light => Ultra Violet => X-rays => Gamma rays
The higher the frequency of an EM wave, …?
The higher the frequency of an EM wave, the more energy it transfers
What are EM waves made up of?
Oscillating electric and magnetic fields
What are alternating current (a.c.) made up of and what do they produce as charge oscillate?
Made up of oscillating charge.
As charges oscillate, they produce oscillating electric and magnetic fields, i.e. EM waves
What happens in a radio transmitter and receiver?
Transmitter - charges (electrons) oscillated to create radio waves
Receiver - radio waves absorbed. Energy carried by waves is transferred to electrons in material of receiver, causing electrons t oscillate and generate an a.c.
What are radio waves mainly used for?
Communication and broadcasting
Why can long-wave radio be received halfway around world?
Long wavelengths bend around curved surface of earth
Why can short-wave radio be received at long distances from transmitter like long-wave radio?
The waves are reflected by earth’s atmosphere
Why do satellites use microwaves or high frequency radio waves instead of short-wave radio?
They can pass easily through earth’s watery atmosphere whereas short-wave radio are usually reflected
Why do microwave ovens use a different, longer wavelength compared to satellites?
In communications, it needs to pass through earth’s watery atmosphere whereas in ovens, it needs to be absorbed by water molecules in food
How do microwave ovens heat up food?
Microwaves used to penetrate up to few cm into food before being absorbed and transferring energy to water molecules i food, causing water to heat up. Energy from water transferred to rest of molecules in food by heating
What is infrared radiation used to do?
Used to increase or monitor temperature
How are infrared cameras used to detect IR radiation and monitor temperature?
Camera detects IR radiation and turns it into an electrical signal, which is displayed on screen as picture (thermal imaging)
What uses visible light?
Photography; photographic film and cameras
