Physics 2 (P2) 2013/14 WJEC

Forces
1. Magnetic
2. Push
3. Weight
4. Upthrust
5. Pull
6. Resultant
  1. If the RF on a stationary object is zero, then it will NOT move
  2. If the RF on a stationary object is NOT zero, then the object will ACCELERATE
  3. If the RF on a moving object is zero, then it is moving at a STEADY SPEED
  4. If the RF on a moving object is NOT zero, then it will ACCELERATE
Energy
1. Kinetic (movement)
  1. 1/2mv(squared)
2. Thermal (Heat)
3. Sound
4. Chemical
5. Nuclear
6. Magnetic
7. Electrical
  1. The rate of transfer of electrical energy by a device is called the electrical power, P, measured in Watts
    1. It can be calculated using the equation; P=VI or the equation P=I(squared)R
8. Gravitational Potential Energy (GPE)
Inside the nucleus
1. Protons
  1. Positively charged particles
2. Neutrons
  1. Neutral Particles
  2. Isotopes, nuclei with the same number of protons but different numbers of neutrons
    1. The different isotopes are often written as 'Pb-208', 'Pb-207' etc. where the number refers to the nucleon number
3. Electrons
  1. Outer shell electrons
    1. The group number gives the number of electrons in the outer shell
    2. The period indicates how many shells of electrons the atom has.
      1. Distance, Speed and Acceleration
        Distance
        measured in metres,m
        How far the object travels
        How far the object is away from a certain point
        The motion of objects can be described and analysed using graphs of motion, see Graphs
        Velocity
        A measure of how fast or slow the object is going in a given direction
        Speed in a given direction
        Measured in m/s in a given direction
        Acceleration
        Measured in metres per second per second, m/s(squared)
        The rate that the object is speeding up or slowing down, which is the rate of the change of velocity
        Can be calculated using the equation; Acceleration=change in velocity / (divided by) time
        Example: Calculate the speed of a horse that gallops 200m in 16s
        Answer: speed=distance/time=200/16=12.5m/s
        Speed
        Measured in metres per second, m/s
        A measure of how fast or slow an object is moving
        Q
4. A,Z,X notation
  1. The number of protons in the nucleus is called the proton number, Z
  2. The number of protons plus the number of neutrons is called the nucleon number, A
    1. The values of Z and A are often shown using A,Z,X notations, where X is the chemical symbol for the atom in question
Electricity
1. Circuits
  1. Series
    1. Current is the same at any point in the circuit
    2. All the components in a series circuit have the same current flowing through them
    3. The total potential difference of the cells is the sum of the individual cells
    4. The potential difference of the supply is shared between the components
    5. The total resistance is the sum of all the individual resistors or components
    6. Can only follow 1 pathway or course
  2. Parallel
    1. The current splits when it reaches a junction
    2. No current is lost at a junction
    3. Total current into the junction= total current out of the junction
    4. Christmas tree lights
    5. Houses use Parallel circuits
    6. Most house lights use Parallel circuits
    7. Safer
      1. The voltage is the same for all components
      2. Each part of the circuit can be protected by its own fuse or circuit breaker and controlled by its own switch
    8. Easier to add new circuits
      1. Easy to work out the total current being drawn by the different parts of the circuit
2. Voltage
  1. The voltage across components in a circuit is measured in volts using a voltmeter
  2. Voltmeters are always connected in parallel across components
  3. In parallel circuits the voltage is the same across each of the bulbs
  4. The resistance of a variable resistor can be changed, in order to vary the current through, and the voltage across, a fixed resistor
    1. For fixed resistors (and wires at a constant temperature), voltage and current are proportional to eachother-- doubling the voltage will double the current
      1. Resistors
        For components such as filament lamps, the resistance changes with current. The resistance of a filament lamp increases with current, so the slope of the voltage-current graph increases
4. George Ohm
  1. The current, voltage and resistance of electrical and electronic components are related to each other. The physicist George Ohm investigated this in 1827
  2. We summarise his findings using the equation; current, I (amps)= voltage, V (volts) / divided by resistance, R (ohms). I= V / (divided by) R
    1. This equation can be used to calculate any one of the three variables, provided that we know the other two
      1. Example question... A 20 ohm fixed resistor has a voltage of 12V across it. Calculate the current through it
      2. Answer: I=V / divided by R = 12 / 20 =0.6A
      3. George Ohm
Graphs
1. Distance-Time graphs
  1. Used to show the distance and time taken in a journey
  2. An increasing in gradient straight line means the object is going at a steady speed
  3. Flat sections mean the object is motionless, ie stopped
  4. To find the speed of an object there are two methods...
    1. Use the formula; Distance/time (/ meaning divided)
    2. Look at the area under the section of the graph you are calculating the speed of and then apply the formula.
2. Velocity-Time graphs
  1. Shows the velocity and the time taken of an object
  2. To calculate the acceleration use the equation; Final Velocity-Initial velocity / (divided by) time
  3. acceleration measured in m/s squared
  4. A - sign in front of the final answer for acceleration indicates that it is deceleration
  5. An increasing gradient on the graph indicates steady acceleration
  6. A flat section indicates steady velocity
  7. The steeper the gradient of an increasing line, the greater the acceleration
  8. A decreasing gradient indicates deceleration
Radioactivity
1. Nuclear Radiation
  1. Some types of atom are radioactive
    1. This means that the nucleus of the atom is unstable and can break apart, emitting ionising radiation
      1. This can be in the form of alpha, beta or gamma radiation
  2. Remember; When we talk about radioactivity or nuclear radiation, it's radiation that's coming from the nucleus of the atom
2. See inside the Nucleus
3. Alpha
  1. Alpha particles are helium nuclei
  2. They are the most ionising and least penetrating form of nuclear radiation
  3. They are absorbed by a thin sheet of paper or by skin
  4. Can cause concern within the public becuase if the alpha particles are absorbed by the skin, they can ionise cells in your body
  5. An alpha particle is made of 2 protons and 2 neutrons
  6. An alpha particle is made up of the same amount of protons and neutrons as a helium particle
    1. An alpha particle has a charge of 2+
      1. An alpha particle has a mass of 4
    2. In an electric field, alpha is deflected slightly towards the negative plate
    3. In a magnetic field Alpha is deflected slightly and opposite to beta
  7. Alpha radiation can travel a few cm's in air
    1. Alpha radiation can be absorbed/stopped by paper/skin
4. Beta
  1. A beta particle is ejected from the nucleus
  2. A beta particle is made of an electron
  3. The charge of this particle is -1
  4. The mass of this particle is so tiny that we count it as 0
  5. Beta particles can travel up to a metre in air
  6. Beta particles can be absorbed/stopped by a few (around 5) millimetres of aluminium
  7. In an Electric Field, a Beta particle is very deflected toward the positive plate
  8. In a magnetic field, a Beta particle is deflected most
5. Gamma
  1. A Gamma wave is an electromagnetic wave
  2. Gamma waves have no mass or charge
  3. Many resources have claimed that Gamma Waves can range over many km in air, or could even be unlimited
  4. Gamma waves can be absorbed/stopped by a few cms of lead or a few feet of concrete
    1. 1. Beta Decay
        A beta particle is an electron
        When an unstable nucleus emits an electron, a neutron in its nucleus changes into a proton and an electron. The electron is emitted
        For example
  5. In an electric field Gamma waves are not deflected at all
  6. In a magnetic field, Gamma waves are not deflected at all
  7. Gamma rays are the least ionising and the most penetrating
6. Half Life
  1. The decay of every radioactive material follows the same pattern. The activities and the half-lives may be very different, but the shape of the decay curve is always the same
  2. There are two definitions of Half Life
    1. 1.The time it takes for half the number of atoms in any sample to decay
    2. 2. The time it takes the count rate from a radioisotope to decrease by 50%
  3. Example; A radioisotope has a half life of 12 minutes, what fraction of the radioisotope will be left after 1 hour?
  4. Example Questions answer: 1/32
  5. An Isotope is an element with the same number of protons but a different number of neutrons
7. Alpha Decay
  1. When an unstable nucleus emits an alpha particle it loses 2 protons and 2 neutrons
    1. For example; Radium-226 decays by alpha emission, 226/88 Rn --> 222/86 Rn+ 4/2 He
  2. Note: The atomic and mass numbers on both sides of the equation balance
  3. An Alpha particle is emitted in Alpha decay
  4. A,Z,X notation; A decreases by 4, Z decreases by 2

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