Detecting Ionising Radiation

Detecting Ionizing Radiation

In this topic I’ll discuss how to detect the ionizing radiation. There are two ways by which we can detect this radiation. These are as following:-

1. Photographic film
2. Geiger Muller tube

Photographic Film

Long ago, scientists used to believe that when some uranium is placed over a photographic film and exposed to sunlight, the uranium will emit x-rays. But on an experiment, it showed that x-rays are being emitted even when uranium over the photographic film isn’t exposed to sunlight. That is, when an ionizing radiation is exposed on a photographic film, there is an image formed on the photographic film because ionizing radiation can make the photographic film fogged.

Uses of photographic film to detect radioactivity

In radioactive places like in nuclear reactors, scientists or technicians who work with radioactive materials, wear a badge with a photographic film inserted in it. If the film becomes fogged, they understand that the scientists or workers are exposed to certain excess amount of radiation. Then they move out from there.

Geiger Muller tube

The diagram of a Geiger Muller tube is drawn above. There is history behind the invention of Geiger Muller tube which you’ll find in the web. The GM tube has a thin window made of mica. The GM tube contains a special mixture of gases at very low pressure. This gas molecules or atoms are ionized when ionizing radiations get in and interact with them and produce a pulse of current. This pulse of current passes to the detecting circuit and detecting circuit gives us the count rate.

Activity

Number of disintegration per second is known as activity.

Unit of activity is Becquerel (Bq).

Background Radiation

Background radiation is a low level ionizing radiation that is produced all the time. Like if a Geiger Muller tube is placed over a table inside a room and switched on, it will start counting the rate of radiation because the color paint on the wall contains uranium and even if there is a human, from his body the ionizing radiations can be produced because there are also chemical reactions going on inside the human body and some chemicals might be unstable that can be ionizing. So even there are some natural and artificial radiations going on that we can’t see because radiations cannot be seen directly by clear human eyes. But ionizing radiations occur all the time and the Geiger Muller tube can count these radiations. Some sources of background radiations and the % effect of them are given below.

Source                                                                                             Effect

Radon gas……………………………………………………………………… 50%

Ground and Buildings………………………………………………………14%

Medical…………………………………………………………………………..14%

Cosmic ray………………………………………………………………………10%

Food and drinks………………………………………………………………11.5%

Nuclear reactor……………………………………………………………....0.3%

Others…………………………………………………………………………….0.2%

Astronomy

Astronomy

In ancient times, when science wasn’t much cared of, people used to believe that the earth, or the ground they’re standing on, is flat and that under the ground, there are five cows and over their spikes, the ground is standing and we are all standing over the ground. When a cow bends down a little to take some water, then the earth quakes!

They also believed that over the sky is a huge monstrous container and at the sides in the inner of the container, is some mud attached. This container is filled with water (as it was thought on those days). When the mud is moved a little, the water escapes from the container and falls as rain!

These are two of the crazy belief of the ancient age. Later astronomical scientists proved that these beliefs are actually crazy. From then on science started keeping on innovating. Those people of that age never tried to understand or even if they tried to, if we’re standing on the ground and the ground is standing over the cows’ spikes, then over what are the cows standing on?!!! Or if where does the water come from that in the container over them?!!!

Now keep on going with the definitions…

Solar system: 8 planets are orbiting the sun in an elliptical path. The sun and the planets are altogether known as solar system.

Gravitational field strength: Gravitational force on 1kg mass is known as gravitational field strength.

Luminous object: These objects which emit light are known as luminous object. E.g. Sun, Stars.

Non-luminous object: Objects that can’t emit its own light is known as luminous object. E.g. Planets, Moons.

Gravitational pull: Gravitational pull on nearest planet is highest. If gravitational pull is large, the motion is faster and the path is more curved. Like the path that Mercury has more curved path towards the Sun than Neptune.

Ideal Transformer

Ideal Transformer

*[Ideal transformers are such transformers that we imagine to be 100% efficient in transforming assuming that none of the current input is wasted in such as heating, etc. Where there is no loss of energy. That means that the voltage input=voltage output. So there is no loss of voltage. But, this is only used for calculations. Such transformers are just imagined transformers. There is no such ideal transformer in practical life. But, physicists imagine this because of the factor for calculation. Hope you got that]

If the efficiency of the transformer is 100%, that transformer is known as ideal transformer.

This equation is applicable for only ideal transformers (hope you got it why there is an ideal transformer in the minds of the physicists).

*[Now let’s solve a problem depending on the equation we just learned]

Problem 1:- A transformer has 100 turns on its primary coil and 500 turns on its secondary coil. If an alternating voltage of 10v is applied in the primary coil, what is the voltage across the secondary coil?

Problem 2:- Input power is 6w. Calculate input and output current.

Problem 3:- Input current across the primary coil is 20A. Power is 250w. Number of turns in the primary coil is 1000. If output current is 2A, calculate the number of turns in the secondary coil.

Transformer and National Grid

*[Have you ever seen pyramid-like power grid towers with lines of current carrying wire attached to them while you travel from one city to another? I hope you do. These things are called the national grid. Whatever electricity produced in a country, privately or by the government, is controlled and distributed by the government by the National Grids. The national grids transport electricity from one city to another.]

Fig:- A visual template of how electricity is produced and supplied.

*[Let’s take it thus that electricity is being produced by a power station. The huge transformers you’ll see if you visit the power station are called step up transformers. They transport the large amount of electricity produced to the government. Then the government supplies electricity by the national grid. Before it directly enters your house, it is brought down into minimum by step down transformers. These transformers you’ll see as you go out of the main gate of your house, look around, you might see some boxes of like electric related devices over pillars. These are placed after some yards of every streets and roads. After the electricity passes the step down transformer, it enters your house and you start using it]

*[Here the electricity transporting through the wire from the step up transformer is very high. So when transporting, some power is wasted as heating the surface of the wire. To reduce this wastage (though not completely), we reduce current and increase the voltage and for this reason the step up transformer is used in the power station to transfer electricity to the national grid. You’ll come to know how it reduces wastage when you’ll study A’ Level after learning and understanding the equation.

Generators

Generators

Motors are devices that use electricity to create motion.

Generators are devices that use the motion of something to produce electricity. There’s a small kind of generator that’s familiar to almost every one of you, the dynamo fitted over the front wheel of your cycle.

Small generator/Dynamo

Fig:- Sorry that I couldn’t draw that thing accurately, but this picture is available in the web and those of you who have the book, see page 192.

An example of a small generator is the dynamo. Usually we use dynamo in the bicycle or in the different motor vehicles.

When a cyclist paddles, the wheels rotate. When wheels rotate, magnet inside the dynamo spins. It produces magnetic flux linkage cut. An induced emf is produced across the coil.

*[The dynamo is a small generator, so we’re using a small and a less stronger magnet that can rotate. But in large scale electricity generator, we can’t make so big magnets rotate. That’s why we place two of the magnets of North and South poles a little apart and in between of them we let rotate the coil, producing voltage.]

*[Big, large scale generators are called alternators.]

Alternator

A generator that produces A.C. is known as alternator.

In alternator, coil rotates between two magnets. This rotation produces magnetic flux linkage cut and an induced voltage is produced across the coil. We use slip ring to make complete rotation. Frequency of the alternating current depends on the number of rotation of the coil in one second. If an alternator rotates twice in a second, the frequency of the alternating current it produces is 2Hz (2 cycles per second).

Transformers

A transformer is a device which can transfer voltage by using the principle of electromagnetic induction (you’ll come to know about this principle in details at A’ Level).

Fig:- This is a diagram of the inside of a transformer.

*[You will see many transformers at your living area on the roads and streets.]

There are two coils in the transformer. One is primary coil and another is secondary coil. Input signal(current) is connected in the primary coil (input signal must be an alternating current). There is a flux linkage change due to the alternating current. This change in flux linkage cut in the secondary coil. This flux linkage cut produces induced emf in the secondary coil. There are 2 types of transformers.

1. Step up:- If output voltage is larger than input voltage, that transformer is known as step up transformer.
2. Step down:- If output voltage is smaller than input voltage, that transformer is know as step down transformer.

Electromagnetic Induction

Electromagnetic Induction

Fig:- [As you can see, a non current carrying wire is hold down on the magnetic field that is created by placing two magnets of opposite poles a little close apart.]

Magnetic Flux Linkage

The intersecting point between magnetic flux and wire is known as magnetic flux linkage.

*[This intersection is shown in the above picture as a red dot between the flux line and wire.]

Flux Linkage Cut

If you move the wire or any of the magnets, the magnetic flux linkage alters. This is known as flux linkage cut.

*[Like if you try to move the wire from its stationary position to up or down, or either side, or if you move the magnets anyway, then the contact breaks and this is known as Flux Linkage Cut.]

Electromagnetic Induction

E.m.f.:- Electromotive force/Voltage

When there is a magnetic flux linkage cut in the wire, there is an induced e.m.f. (voltage) produced in the wire. This phenomenon is known as electromagnetic induction. The ways of increasing e.m.f. in a wire:-

1. Moving the wire more quickly.
2. By using a stronger magnet.
3. Wrapping the wire into a coil.

*[This voltage is powerful and strong]

Induced E.m.f. and coil

Fig:- *[I’m sorry because there isn’t enough light appearing in the image above but those who have book, pls have a look at page 190, and those who don’t have book, pls struggle, remember, no pain, no gain.]

When we move the magnet backward and forward inside the coil, the voltmeter gives us a reading due to electromagnetic induction (as a current is produced). Ways of increasing the induced e.m.f.:-

1. Using stronger magnet.
2. Moving the magnet faster
3. Using coil with more turn.
4. Using coil with larger cross-sectional area.

Faraday’s law of electromagnetic induction.

 The size of induced emf (voltage)across the end of a wire (coil) is directly proportional to the rate at which the magnetic lines of flux are being cut.

*[There’s something like Lenz’s law, you’ll get better and clear understanding if you ask it to your teacher]