7b) Radioactivity

Structure of Atoms:

The nucleus of an atom contains protons and neutrons. It makes up most of the mass of an atom, but virtually no space - tiny. in a nucleus are called the atomic number or proton number. The total
The electrons are negatively charged and are small. They are outside of the atom and take up the most space, giving it's overall size. 
The number of protons in a nucleus are called the atomic number or proton number. The total number of protons and neutrons in the nucleus are called the mass number or nucleon number.

Isotopes:
Have the same number of protons, but different number of neutrons (mass number/nuclear number)

Alpha Particles:

• made of 2 protons and 2 neutrons (like Helium) and are big, heavy and slow moving 
• don't penetrate far (easily stopped) 
• Strongly ionising 
• Electrically charged --> deflected by electric and magnetic fields
• emitting alpha particles decreases the atomic number by 2 and the mass number by 4 

Beta Particles

• Electron emitted from the nucleus of an atom when a neutron turns into a proton and an electron. When a beta particle is emitted the number of protons increases by 1, so the atomic number increases too
• Move quite fast and are small 
• penetrate moderately, and moderately ionising 
• Charged --> deflected by electric and magnetic fields 

Gamma rays

• no mass, just energy
• penetrate along way 
• weakly ionising 
• no charge and so isn't deflected 
• gamma emissions happen after alpha or beta decay --> no effect on atomic or mass number 

Penetrating power

Alpha --> blocked by paper, skin or a few cm of air 

Beta --> stopped by thin metal

Gamma --> thick lead or concrete 

Complete balanced nuclear equations:

Alpha decay

Beta decay

How to detect ionising radiation:

• radiation imprints on camera film 
• Geiger-Muller detector (GM counter) beeps in the presence, the more radiation the more frequency it beeps 

Where is it from?

Half Life:

• time taken for half of the radioactive atoms now present to decay 
•  

Uses and Dangers:
Alpha
detect a fire - ionises air, small current when smoke enters --> alarm goes off
Change cells - don't cause harm outside body, but most inside 

Beta
testing thickness - intensity proportional to paper thickness 
leaks in pipes - put in use GM counter
Change cell - can penetrate deeper into the body, not ionising 

Gamma
detect cracks - like an X ray 
Sterilisation - go through packaged source 
Medical imaging - inject radioactive tracer 
Radiotherapy - kill cancer cells 
Change cells - passed through flesh, bones absorb gamma rays (most) and not very ionising 

7a) Units

• Becquerel (Bq) 
• Centimetre (cm) 
• Hour (h) 
• Minute (m) 
• Second (s) 

Section 7

Radioactivity and Particles

6d) Electromagnetic Induction

Electromagnetic Induction: The creation of a voltage (and maybe a current) in a wire which is experiencing a change in magnetic field.

To get a bigger voltage....
Increase the strength of the magnet
Increase the speed of movement
Increase the number of turns on the coil

You can reverse the current direction:
reverse the magnetic field by flipping the magnet
switching/ change the direction of wire movement

Only get an induced current if it is part of a complete circuit, otherwise it would be an induced voltage (will always be an induced voltage)

Factors that increase the amount of electricity being produced: strength of magnetic field, number of coils in wire, speed of rotations

Paper Two- Transformers 

Is a device which can increase or decrease the value of an alternating voltage by having different number of turns on input and output sides. It consists of two coils wound round an soft iron core. 

    

Step-Up Transformers

• increases the voltage by more turns on the secondary coil than primary

Step-Down Transformers

• decreases the voltage by having more turns on the primary coil than secondary

input(primary)voltage/ output(secondary)voltage =  primary turns/ secondary turns 

Vp/Vs = Np/ Ns 

Transformer efficiency:

= Power output from secondary coil / Power input to primary coil 

= (I_sV_s) / (I_pV_p) x 100% 

(I_sV_s) / (I_pV_p)

 when a transformer is supplying current, it is almost 100% efficient 

6c) Electromagnetism

Magnetic fields in current-carrying wire:

• an electric current in a material produces a magnetic field around it 
• the larger the electric current, the stronger the magnetic field 
• the direction of the magnetic field depends on the direction of the current 

Paper Two-

Straight wire, Flat circular coil and Solenoid:

The magnetic field around a straight wire is circular:

The magnetic field around a flat circular coil ellipses (egg-shaped):

The magnetic field around a solenoid  is electromagnet: 

If something with a charge is moving across a magnetic field it will 

experience a force from the field, unless it's parallel. 

D.C. Electric Motor (simple):

• wire in magnetic field 
• force turns a 'split ring communicator' ---> charge goes from brushes in wires 

      Four factors

1. more current 
2. more turns on coil 
3. stronger magnetic field 
4. soft iron core 

Loudspeaker:

• force pushes current away from field, pushes core which makes sound ---> cone vibrates 

The left hand rule:

Helps to figure out the thrust/motion, field and current of the wire to then work out which way the force is acting.

Wire in magnetic field increase (<) current = more force on wire 

Wire in magnetic field increase (<) strength = more force on wire 

6b) Magnetism

 Paper Two- 
Repel and attract

Opposite poles attract to one another:


Same poles repel one another:


Magnetic substances can also be attracted by a magnet

Properties of a magnetic material

Magnetically hard material ---> retains its magnet properties for a long period of time/permanent. hard to demagnetise

Magnetically soft material ---> loses its magnetic properties almost as soon as the magnet field leaves

Magnetic field lines:

• represent shape and direction of magnetic field 
• gives an idea of magnetic field 

Induced Magnetism;

When a magnet is brought near a magnetic material then the material will acts as a magnet because the magnetic field encourages them to align and form poles. Examples: iron, cobalt and nickel. 

The closer the magnet, the stronger the induced magnetism becomes. 

Experiments to find the magnetic field pattern of a permanent magnet and two bar magnets:
Can use multiple compasses or iron fillings to see the magnetic field.

     

Hold two opposite poles close together so that they attract
and makes a uniform magnetic field:

6a) units

• Ampere (A) 
• volt (v) 
• watt (W)