Electricity

Electricity Glossary Slide 3-4: Electrical Charge Slide 5: Electrical Current Slide 6: Resistance Slide 7: A.C. and D.C. Slide 8 Potential Difference/Voltage Slide 9: Series and Parallel Circuits Slide 10: Current in Series Slide 11: Current in Parallel Slide 12-14: Voltage in Series Slide 15: Voltage in Parallel Slide 16: Electrical Power Slide 17: Electrical Power (extra)

Electrical Charge + + There are 3 types of charge in Physics – positive, neutral and negative. Protons have a positive charge. Neutrons have a neutral charge. Electrons have a negative charge. - - When two like charges are placed close to one another they repel (like two protons). When two like charges are placed close to one another they repel (like two electrons). + - + - When two opposite charges are placed close to one another they attract (like a proton and electron)

Electrical Charge If the wires are made of a conductor, like copper, then it is possible for the electrons to flow around the circuit once a battery is connected. This happens because the battery has a negative terminal which repels electrons and a positive terminal which attracts electrons. Below is a series circuit with a battery in it and connecting wires. The wires are made up of billions and billions of atoms which all have electrons orbiting them. As one electron moves it repels the electron next to it and so on, meaning all the electrons start to flow around the circuit as a result of the battery being placed in it. Negative Terminal Positive Terminal + - - - - - - - - - - - - - - - - - - - - - - - -

A 1.9 A - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Electrical Current Current is the amount of electrical charge which passes a point every second. Current = the amount of charge passing a point per second Current = charge/time I = Q/t In total, 19 charges managed to pass within the 10 seconds. So, to work out the current... Imagine our copper wire again. If we look inside the wire we would see the electrons (negative charges) again. s I = Q/t I = 19/10 I = 1.9 A If we placed an ammeter on any part of this wire it would read 1.9A when the current was flowing. From the red dot, count how many charges pass in 10 seconds. A (amperes) C (coulombs) Time (s) 1.9 charges per second A 10 9 7 6 8 1 4 5 3 2 1.9 A - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

A 1 A - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Resistance Resistance decreases the current in a circuit. It slows down the flow of charge. Resistance turns electrical energy into heat energy. This is why television and laptops etc. can become warm. The symbol for a resistor is, If we were to consider our electrical wire in a circuit again but with a resistor attached this time then we would notice a decrease in the flow of charge so a smaller value on our ammeter. A 1 A - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

A.C. and D.C. These are the symbols you are likely to see for a D.C. supply, D.C. stands for direct current. D.C. is when the current flows around a circuit in one direction. A.C. stands for alternating current. A.C. is when the current changes direction, back and forth, several times a second. + - + - + - d.c. These are the symbols you are likely to see for an A.C. supply, a.c. (no + or - ) (terminals with sine wave in between)

Potential Difference/Voltage Voltage is the energy per charge. “Potential difference” is the same as voltage. Imagine a 3 V battery in a circuit. 3 V For any charge which passes through the battery it will receive 3 joules of energy. + - 0 J 3 J 3 J of energy per charge = 3 V

Series and Parallel Circuits + - A series circuit has only one path for electrons to flow around. A parallel circuit has more than one path for electrons to flow around. only path + - first path second path

Current in Series - + 2.8 A 2.8 A 2.8 A As there is only one path for electrons to flow around, the current is the same everywhere in a series circuit. 2.8 A

Current in Parallel As there is more than one path for the electrons to flow around the current may change in different paths. + - In a parallel circuit the current is different depending which path you are looking at. The current close to the power supply is equal to the sum of the current in all the paths. The resistance in each path determines the current in that path. In this example, the top path (0.9A) has a higher resistance than the bottom path (1.5A). This is why the current is less. 2.4 A 0.9 A Junction where electrons meet up again. Junction where electrons split up into different paths. 1.5 A

- + Voltage in Series 6 V 0J 6J It is placed across the bulb to check how much energy charges have before entering and how much they have after exiting. The difference is the energy the charge gave the bulb. If a voltmeter was placed across the bulb it would tell us how much energy each charge gives the light bulb. For simplicity, I will remove all the charges except one. I will also slow the charge down so you can easily see what’s going on. In our circuit we will also place one bulb. When the charge passes through, it gives up all the electrical energy it received from the battery so the bulb can convert it into light (and heat). Remember, voltage means the energy per charge. So a 6 V battery would give out 6 J (joules) of energy per charge. 6 V

- + Voltage in Series 6 V 3 V 3 V 0J 6J If we place voltmeters across each of our bulbs they would give the following readings, Now lets consider two bulbs which are identical (have the same resistance). 3 V 3 V 3J 3 joules of energy per charge is given to the bulb. Less energy per charge means dimmer bulbs.

- + Voltage in Series 6 V 4 V 2 V 0J 6J If we place voltmeters across each of our bulbs they would give the following readings, The voltage across all appliances in a series circuit is equal to the supply voltage. Now say the bulbs had different resistances. If the first bulb had twice the resistance of the second bulb it would get twice the voltage (as V = IR and the current is the same everywhere). 4 V 2 V 2J The first bulb gets twice as much energy per charge so is twice as bright as the second bulb.

This means the energy per charge (voltage) is the same for each bulb. Voltage in Parallel 6 V + - Any charge that goes through the first branch gives up all its energy to the bulb in that branch. The bulbs on each branch/path of the parallel circuit are identical (same resistance). This means the energy per charge (voltage) is the same for each bulb. The voltage across each branch in a parallel circuit is equal to the supply voltage. The charges can only choose one branch before going back to the battery to get more energy. Any charge that goes through the second branch gives up all its energy to the bulb in that branch. 6 V 6 V

Electrical Power Power is the energy produced per second. Power = Energy/time P = E/t A 60 W bulb gives off 60 joules of energy per second. A 100 W bulb gives off 100 joules of energy per second. s W (Watts) J (Joules) A 2200 W kettle gives off 2200 joules of energy per second.

Electrical Power (Extra) Power is the energy produced per second. Voltage is the energy per charge. Current is the number of charges passing a point per second. Voltage = Energy per Charge V = E/Q Current = Charges per second I = Q/t 6 V 12 V Voltage x Current = V x I Higher voltage = more electrical energy given per charge per second = more light energy produced per second = more power = brighter bulb Higher current = more electrical energy given per second = more light energy produced per second = more power = brighter bulb = E/Q x Q/t = EQ/Qt Power = Voltage x Current P = VI = E/t = Power