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## AQA Additional Physics Revision

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**How do you calculate acceleration from a speed-time**graph?Acceleration = change in velocity/time taken for the changee.g. 10m/s = 2m/s2 5s**Be able to plotVelocity-time graphs**• Bbcbitesize • Science > Additional Science (AQA) > Forces and motion > Representing motion**F=MA**• See bbcbitesize additional science aqa physics • Forces and motion**Elastic potential energy is stored in an object when a force**change its shape**Kinetic energy= ½ x mass x speed**• Bbcbitesize • Science > Additional Science (AQA) > Forces and motion > Kinetic energy**Momentum=mass x velocityMomentum has both magnitudeAnd**direction**When a force acts on a body a change in momentum**occursMomentum is conserved in any collision/explosion provided no external forces act**Electrically charged bodies exert forces on each other;LIKE**CHARGES REPELUNLIKE CHARGES ATTRACT**Simple diagrams showing how a lightning conductor works**Lightning conductors work to protect tall buildings from lightning strike. This is by providing an easier path for current to flow to the earth other than through the building. It consists of a thick copper strip of very low resistance connected to a large metal plate deep in the damp earth.**To interpret and draw circuit diagrams using standard**symbols**graphs for a resistor at constant temperature, a filament**lamp and a Diode**Potential difference (V)=current(A) X resistance(Ohms)V=IR**• Pd Current resistance • 2v .......... 2 ohms • ......... 1.5 amps 2 ohms • 4v 2 amps .......... • .......... 3 amps 2 ohms • A p.d. of 4v is applied to two resistors (6 ohms and 2 ohms) connected in series • What is • 1. the combined resistance • 2.the current flowing • 3. the p.d. across the 6 ohm resistor**A p.d. of 4v is applied to two resistors (6 ohms and 2 ohms)**connected in series - What is1. the combined resistance2.the current flowing3. the p.d. across the 6 ohm resistor • Pd Current resistance • 2v .I amp 2 ohms • .3v 1.5 amps 2 ohms • 4v 2 amps 2 ohms • .6 v 3 amps 2 ohms • 1. 6 + 2 = 8 ohms (NB only in series circuits) • 2. I = V/R = 4/8 = 0.5 amps • 3. V = IR = 0.5 x 6 = 3V**For components connected in seriesThe total resistance is**the sum of the resistance of each componentThere is the same current through each componentThe total pd of the supply is shared between the components**For components in connected in parallelThe pd across each**component is the sameThe total current through the whole circuit is the sum of the currents through the separate components**Cells and batteries supply current which always passes in**the same direction. This is called direct current (dc)**An alternating current (ac) is one which is constantly**changing direction. Mains electricity is an ac supply. In the UK it has a frequency of 50 cycles per second (50 hertz)**UK mains supply is about 230 voltsTo determine the period**and hence the frequency of a supply from the diagrams of oscilloscope traces.**To find frequency 1 period is ~ 3.5 ms or**0.0035sFrequency = 1/0.0035=285 Hz**Find frequency**Each division = 10 ms Each division = 1ms Each division = 5 ms**1 period is 4 x 1 = 4ms**4 ms = 0.004s Frequency = 1/0.004 = 250 Hz 1 period is 4 x 10 = 40ms 4 ms = 0.04s Frequency = 1/0.04 = 25 Hz 1 period is 4 x5 = 20ms 4 ms = 0.02s Frequency = 1/0.02 = 50 Hz THIS IS THE SAME A UK MAINS ELECTRICITY**Questions**• 1. what is the difference between ac and dc current • 2. what is the frequency of UK mains electricity • 3. How does the potential (voltage) vary with each cycle