Topic 7

Radioactivity and Particles

Objectives:

7a) Units

7.1 use the following units: becquerel (Bq), centimetre (cm), hour (h), minute (min), second (s)

7b) Radioactivity

7.2 describe the structure of an atom in terms of protons neutron and electrons and use symbols such as ¹⁴₆C to describe particular nuclei

7.3 understand the temrs atomic (proton) number, mass (nucleon) number and isotope

7.4 understand that alpha and beta particles and gamma rays are ionising radiation emitted from unstable nuclei in a random process

7.5 describe the nature of alpha and beta particles and gamma rays and recall that they may be distinguished in terms of penetrating powwer

7.6 describe the effects on the atomic and mass number of a nucleus of the emission of each of the main types of radiation

7.7 understand how to complete balance nuclear equations

7.8 understand that ionising radiation can be detected using a photographic film or a Geiger-Muller detector

7.9 recall the sources of background radiation

7.10 understand that the activity of a radioactive source decrease over a period of time and is measure in becquerels

7.11 recall the temr 'half-life' and understand that it is different for different radioactive isotopes

7.12 use the concept of half-life to carry out simple calculation on activity

7.13 decribe the uses of radioactivity in medical and non-medical tracers, in radiotherapy and in the radioactivbe dating of archaelogical specimins and rocks

7.14 describe the dangers of ionising radiation, including:

- radiation can cause mutations in living organisms

radiation can damage cells and tissue

the problems arising in the disposal of radioactive waste

7c) Particles

7.15 describe the results of Geiger and Marsden's experiment with gold foil and alpha particles

7.16 describe Rutherford's nuclear model of the atom and how it accounts for the results of Geiger and Marsden's experiment and understand the factors (charge and speed) which affect the deflection of alpha particles by a nucleus

7.17 understand that a nucleus of U-235 can be split (the process of fission) by collision with a neutron, and that this process releases energy in the form of kinetic energy of the fission products

7.18 recall that the fission of U-235 produces two daughter nuclei and a small number of neutrons

7.19 understand that a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei

7.20 understand the role played by the control moderator when the fission process is used as an energfhy source to generate electricity.

Faraday's Lab

This animation is great for demonstrating the physics of electromagnets

Click to Download

6.20 100% Efficiency

Recall and use the relationship (for 100% efficiency):

We know that energy cannot be created nor destroyed so in the case of 100% efficiency the input power must always equal the output power of a transformer
Remember: Power = Current x Voltage

Note: In reality Transformers are roughly 99% efficient

6.19 Turns

Recall and use the relationship between input (primary) and output (secondary) voltages and the turn ratio for a transformer:

The ratio between voltage and turns is shown above, this can be used to predict the output voltage of a transformer. It is worth noting that that because this is a ratio you could place the secondary turns and voltage on top as long as both are on the top or bottom (i.e. Vp and Ns on top would be incorrect)

Example question:

a) This is a step-up transformer because the voltage is being decreased

b)

        

     

        

        

c)

     
 
 
d) 24 Watts of Power is delivered to the lamp [assuming 100% efficiency]
e) 24 Watts [see 6.20]
f)
    

 
 
g) If the transformer is only 50% efficient, half of the energy would be wasted. In order to retain 24Watts of power the primary current must be doubled so that the primary power is 48Watts.

6.18 Transformers in Power Stations

Explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy


After electricity is generated in a power plant it is transformed into very high voltage so that it can be transported across the country through power lines with little energy loss. It is then transformed down to the voltage used in household sockets.

A transformer that increases voltage is called a step-up transform, and a transformer the decreases voltage is a step-down transformer.

6.17 Transformer

Recall the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides

A transformer consists of a circular iron core with input and output coils wrapped around opposite sides. In order for it to work there needs to be a changing magnetic field; this is why DC power cannot be transformed


http://micro.magnet.fsu.edu/electromag/java/transformer/index.html
The Java applet at this URL shows a simple transformer

6.16 Generator

Describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field; also recall the factors which affect the size of the induced voltage

In a generator a magnet is rotating near a coil of wire. This rotatory motion induces a current in the wire generating electricity. On the other hand you could also rotate the wire inside a magnetic field

It is important to note that because of the rotations Alternating Current (AC) is produced