4.4.5 Electromagnetic waves

Question 1

What are the similarities and differences in all EM weaves?

Answer 1

Similarities:
1. Ability to go through vacuum;
2. None of them move matter;
3. All have a magnetic wave and an electrical wave, which are orthogonal, or perpendicular to each-other;
4. In free space, they all travel at c, the speed of light - which is 2.98x10^8m/s;
5. They are all transverse;
6. All can be polarised, reflected, refracted and diffracted;
7. All can have interference lines;
Differences:
1. Wavelength;
2. Frequencies;

Question 2

What is/are the:
- Wavelength;
- Frequency (Hz);
- method of production;
- Method od detection;
- Use(s); 
Of radio waves?

Answer 2

1. 10^-1-10^4;
2. 3x10^9-3x10^4;
3. Electrons oscillated by electric fields in aerials;
4. Resonance in electronic circuits;
5. TV, radio and communications;

Question 3

What is/are the:
- Wavelength;
- Frequency (Hz);
- method of production;
- Method od detection;
- Use(s); 
Of microwaves?

Answer 3

1. 10^-4-10^1;
2. 3x10^12-3x10^9;
3. Magnetron, klystron oscillators, using electrons to set up oscillations in a cavity;
4. Heating effect, electronic circuits;
5. Radar, mobile phones, microwave ovens, satellite navigation;

Question 4

What is/are the:
- Wavelength;
- Frequency (Hz);
- method of production;
- Method od detection;
- Use(s); 
Of IR?

Answer 4

1. 7.4x10^-7-10^-3;
2. 4x10^14-3x10^11;
3. Oscillations of molecules, rom all objects at any temperature above absolute zero;
4. Photographic film, thermopile, heating of skin;
5. Heaters, night vision equipment and remote controls;

Question 5

What is/are the:
- Wavelength;
- Frequency (Hz);
- method of production;
- Method od detection;
- Use(s); 
Of visible light?

Answer 5

1. 3.7x10^-7-7.4x10^-7;
2. 8x10^14-4x10^14;
3. From high - temperature solids and gases, lasers;
4. Photographic film, retina of eye;
5. Sight, communication;

Question 6

What is/are the:
- Wavelength;
- Frequency (Hz);
- method of production;
- Method od detection;
- Use(s); 
Of UV?

Answer 6

1. 10^-9-3.7x10^-7;
2. 3x10^17-8x10^14;
3. from high temperature solids and gases, lasers;
4. Photographic film, phosphors, sunburn (this is only for UV-b, which makes up a small proportion of UV light);
5. Disco lights, tanning studios, counterfeit detection, by detergents;

Question 7

What is/are the:
- Wavelength;
- Frequency (Hz);
- method of production;
- Method od detection;
- Use(s); 
Of X-rays?

Answer 7

1. 10^-12-10^-7;
2. 3x10^20-3x10^15;
3. Bombarding metals with high-energy electrons;
4. Photographic film, fluorescence;
5. Computer aided tomography (CT)

Question 8

What is/are the:
- Wavelength;
- Frequency (Hz);
- method of production;
- Method od detection;
- Use(s); 
Of gamma rays?

Answer 8

1. 10^-16-10^9;
2. 3x10^24-3x10^17;
3. Nuclear decay or in a nuclear accelerator
4. Photographic film, Geiger tube;
5. Radiotherapy (diagnosis and cancer treatment);

Question 9

What is the difference between x rays and grammar rays? Apply this to other EM waves.

Answer 9

They are often identical in terms of their energies, wavelengths and frequencies: the main difference is where they come from:
X rays: accelerated electrons OUTSIDE the nucleus;
Gamma rays: emitted from INSIDE the nucleus of the atom;
2. With other EM waves: it is no possible to say when a radio wave becomes a microwave, for example - where the ranges in their wavelength and frequencies overlap - the em spectrum is really just one long, continuous line.

Question 10

How did theoretical physics and experimental physics come together in the panicle of em discovery?

Answer 10

In the mid 19th c, little was known about em radiation (only IR was well documented) so:
Theoretically
- Physicist James Clerk Maxwell formulated the Maxwell equations that related electric and magnetic fields to show that em waves were theoretically possible.
Experimentally:
- Heinrich Hertz was the first to produce radio waves - X rays were later discovered in 1895
- Gamma rays in 1986
- Microwaves (leading to radar) with the magnetron in the 1930s.

Question 11

What is ionisation in the case of EM waves?

Answer 11

Only UV, gamma and x rays can ionise, which is having enough photon energy to remove an electron from an atom, which starts a chain reaction to cause cancer.

Question 12

What is special about non-ionising radiation and why?

Answer 12

It is relatively safe - as it does not have enough photon energy to ionise cells and cause mutations which leads to cancer.

Question 13

Why can one be sitting indoors, with sunlight streaming through windows for hours and not be sunburnt?

Answer 13

because UV-B is blocked out by the glass in the windows, this is the variety of UV that causes skin damage (cancer and sunburn).

Question 14

How does sun cream work?

Answer 14

it blocks out UV-B, which is the variety of UV that causes skin damage (cancer and sunburn).

Question 15

What are the three varieties of UV light, what do they do, and what are their wavelengths?

Answer 15

1. UV-A: tanning, =99% of UV light;
315-400nm wavelength;
2. UV-B: sunburn and skin cancer;
280-315nm wavelength;
3. UV-C: filtered by the atmosphere - does not reach the surface of Earth;
100-280nm wavelength;

Question 16

When is UV visible to the naked eye? Produce an example.

Answer 16

1. When it is subjected to a substance called a phosor;

2. Example: detergents contain phosors, which is why a white t shirt would appear fluorescent under a night club light.

Question 17

Why is the development in x ray technology only recent? Produce an example of this development.

Answer 17

1. X rays are essentially shadows, and so could only be used for bone imaging (shadow pictures) without a computer up until recently;
2. Computer-aided tomography scans (CT scans)
   These are 3D images of bones, taken from a series of cross-sectional planes
3. Increased contrast and higher resolution in images taken, so that smaller things can be seen (due to computer development);

Question 18

How are x rays produced?

Answer 18

By firing high energy electrons at a copper anode (as the two are oppositely charged). The filament that the electrons are emitted from is heated, and it is done so in a vacuum. As the electrons collide with the heavy metal target, they produce x-rays –which tells us they interact with the electrons in this, and not the nucleus, as there are no gamma rays produced.

Question 19

When is gamma radiation released? Produce an example.

Answer 19

1. Human cost: it is extremely ionising, which can cause cancer.
2. For example, in April 1986 Chernobyl, town of Pripyat - people were affected through contamination rather than irradiation.

Question 20

Name uses of gamma radiation.

Answer 20

1. the sterilisation of medical equipment and edible produce