Topic 6b- Electromagnetic waves Flashcards
What is the electromagnetic spectrum?
The electromagnetic spectrum is a continuous spectrum of all the possible wavelengths of electromagnetic waves
What are the different wavelengths going from lowest frequency to highest
- radiowaves
- micro-waves
- infrared
- visible light
- ultraviolet
- x-rays
- gamma-rays
What is the approximate wavelength of visible light?
10^-7m
What happens if an atom absorbs energy
If an atom absorbs energy, some of its electrons move to higher energy levels within the atom. When each electron falls back down to its original level, an electromagnetic wave is produced
How are electromagnetic waves produced?
When an atom gains energy and it’s electrons move from a highe energy level back down to its original energy level
How are gamma rays produced
Unstable nuclei breaking apart in nuclear decay (emmited from ‘daughter’ nucleus)
How are radiowaves produced?
Using alternating current (AC). As the charges oscillate, they produce oscillating electric and magnetic fields (electromagnetic waves) which is what radiowaves are. The frequency of the radiowave produced will be equal to the frequency of the alternating current.
How are radiowaves recieved?
The reciever absorbs the radiowaves. The energy carried by the waves is transferred to the kinetic energy stores of the electrons in the material of the reciever. This causes the electrons to oscillate and, if the reciever is part of a complete electrical circuit, it generates an alternating current. The current has the same frequency as the radiowave.
What device is used to measure oscillations of a wave?
An oscilloscope
What makes long-wave radio wavelengths suited to their use?
What is their approximate wavelength?
- they can be transmitted and recieved halfway round the world
- this is because they diffract (bend) around the world’s surface and around hills
- this means they can be recieved even if the reciever isn’t in the line of sight of the transmitter
- [wavelength → 1-10km]
What makes short-wave radio wavelengths suited to their use?
What is their approximate wavelength?
- don’t diffract around the Earth’s curve
- can still be recieved at large distances
- reflected between the earth and the ionosphere
- Bluetooth uses short-wave radiowaves
- [wavelength → 10-100m]
What are the properties of TV and FM radio waves?
- must be in direct sight of the transmitter
- don’t travel far through objects
- signal doesnt diffract round hills
What are uses of microwaves (the waves)
- satelite communications (microwaves easily pass through Earth’s atmosphere)
- cooking in microwaves → the waves penetrate up to a few centimeters into the food before being absorbed and transferred into thermal energy
What are uses of infrared radiation?
- innfrared cameras
- cooking
- electric heaters
What are uses of visible light?
- fibre optic cables
What are uses of ultraviolet radiation (UV)
- sun tanning lamps
- security ink
- energy efficient bulbs
What are uses of x-rays and gamma rays?
- medical imaging
- medical treatment (e.g. radiotherapy)
Which EM radiation is the most harmful?
Higher frequency e.g.
- UV
- x-rays
- gamma rays
What is the radiation dose measured in?
sieverts
What does radiation dose take into account
- total amount of radiation absorbed
- how harmful the type of radiation is
- the type of tissue absorbing the radiation
What are opaque objects?
objects that absorb some wavelengths of light and reflect others (e.g. a red apple reflects the red light but absorbs the others)
What is the difference between transparent and translucent objects?
- transparent objects transmit light in straight lines so you can see clearly thorugh them (e.g. clear glass)
- translucent objects transmit light but also scatter it so you can’t see clearly through them (e.g. frosted glass)
What does the temperature of an object depend on?
The amount of infrared radiation it absorbs and emits
What surface will absorb and emit the most infrared radiation?
A matt black surface
What surface will absorb and emit the least infrared radation?
a shiny white surface
How does radiation affect Earth’s temperature?
During the day, more radiation is absorbed than emitted causing it to be warmer, whereas at night more is emitted than absorbed causing the earth to cool
What is a perfect black body?
A perfect black body is an object that absorbs all of the electromagnetic radiation that hits it. No radiation is reflected or transmitted by it.
What is intensity (in reference to wavelengths?)
The power per unit area
What is the correlation between temperature and intensity of wavelength?
As the temperature of an object increases, the intensity of every emmited wavelength increases too.
What is the link between temperature and the distribution of wavelengths from an object?
As the temperature of an object increases, the peak wavelength decreases (i.e. the wavelengths are shorter)
