Physics IGCSE

These cards are to be used for revision of the Edexcel Certificate or IGCSE

• Created by: Gianamar
• Created on: 11-07-12 21:46

Voltage, Current and Resistance

Ohm's Law states that there is a linear relation between voltage, current and resistance. The law states that

V = IR

where V is voltage, measured in volts (joules/coulombs = Energy/Charge), I is the current, measured in amps (coulombs/seconds = Charge/time) and R is resistance, measured in ohms (Ω) (joules.seconds/coulombs).

In a circuit, the voltage is the push that the electrons are being given, like the pressure which causes them to move in the first place. The current is the flow of electrons, and it is defined as the charge of a circuit per second. The resistance is almost like friction. Anything which slows down the flow of electrons around a circuit is a resistor. This causes resistance, which is measured in ohms.

Therefore, as current increases, voltage increases. When resistance increases, voltage increases. A decrease in voltage could be due to either a decrease in current or a decrease in resistance.

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Electromagnetic Induction

Electromagnetic induction is the process by which a voltage (and sometimes a current) are generated by the kinetic energy of a rotating wire in the presence of a magnet.

Electromagnetic induction produces an alternating current which is due to half of the coil rotating towards the magnet's north, and the other half rotating towards the south. The coil changes direction every half turn.

The higher the frequency of the wave peaks in an AC vs time graph created by a Cathode Ray Oscilloscope (CRO), the higher the voltage, and the higher the speed at which the coil is rotating.

To get a higher voltage, you can increase

• The strength of the magnet
• The number of turns of the coil
• The speed of the coil's movement
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Useful Physics Formulae

• V = IR
• P = IV = I²R = V²/R = W/t = E/t
• F = ma
• a = (v-u)/t
• W = Fd = mad
• p = mv
• F = Δp/t
• P.E. = mgh
• K.E. = 1/2mv² = Fd = W
• f = 1/T = v/λ
• v =  λf
• Moment = Force  x  perpendicular distance
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Astronomy

We live in the Solar System. Planet Earth is the third furthest from the Sun. Our Solar System is part of a galaxy called the Milky Way Galaxy, which is amongst billions of others in the Universe. The planets move in almost circular (elliptical) orbits around our star, the Sun due to the force of gravity, which is acting as a centripetal force, and is making the us follow curved orbits.

v = 2πr/T

orbital speed = 2π*orbital radius / time period

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Transformers

Transformers are machines which change voltages. A step up transformer increases output voltage (and decreases output current). A step down transformer takes in a high voltage and decreases it (and increases current).

A transformer is a pure iron core (which is very magnetically permeable), with an input wire (with a given voltage), an output wire and coils on the iron core. If there are more primary coils than secondary coils, it is a step down transformer, decreasing the output voltage. If there are more secondary coils, it is a step up transformer, increasing output voltage.

Vp/Vs = Np/Ns = Is/Ip

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Transformers 6 of 6