Work out the value of the unknown currents and potential differences (voltages). All the lamps are identical.

Resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Resistance is measured in Ohms (Ω) If resistance increases in a circuit the current will decrease (and vice versa) for a constant Voltage supply A resistor is used to convert electrical energy into: Light, Mechanical and Sound energy

Conductors and Resistance Conductivity is related to resistance Materials that are good conductors have a low resistance. Materials that are good insulators have a high resistance.

Thin wires have a greater resistance than thick wires. Long wires have a greater resistance than short wires

Wires create resistance

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Ohm’s Law

V = I R “Ohm’s Law” Is it really a law ? ( I  V ) It works for resistors: V I ( I  V ) (temperature of the resistor remains constant) Does it works for Light bulbs?: Non-Ohmic Resistor The resistance of a filament lamp increases as the temperature of its filament increases due to increased current (more electrons collisions in a confined space…) V I

The basic idea behind regular light bulbs is simple The basic idea behind regular light bulbs is simple. Electricity runs through the filament. The filament resists the electricity, and this resistance turns electrical energy into heat . The heat is enough to make the filament white hot, and the "white" part is light . The filament glows because of the heat. The problem is that heat wastes a lot of electricity. Heat is not light, and the purpose of the light bulb is light, so all of the energy spent creating heat is a waste.

Quantities - Symbols & units Quantity Symbol Unit Current I Amperes A Voltage V Volts Resistance R Ohms Ω

Resistance Investigation Aim: Investigate the effect of increasing resistance has on: Current in a circuit Voltage across a light bulb in your circuit The brightness of the light bulb in your circuit Task: Construct the circuit shown Record your observations for the 3 points above Summarise your findings

Resistance investigation

Rules for Series & Parallel Circuits The current is the same throughout the circuit. The voltages across each component, add to give the total voltage. Parallel The currents through each branch of the circuit add to give the total current. The voltage across each branch of the circuit is the same.

Additional Rules Series As more bulbs are added in series, the current decreases. This is because the total resistance increases. Parallel As more bulbs are added in parallel, the current increases. This is because the total resistance decreases.

  These have no branches or junctions If one bulb breaks, the other bulbs in other branches stay on. Can be turned on and off by a single switch anywhere in circuit If you put more bulbs in they will be dimmer as it is harder for the current to get through- the resistance is higher Switches can be put into the circuit to turn on and off all or part of the circuit. The voltage across each branch is the same and is equal to the voltage across the cell or battery These have branches and junctions   There is more than one path for the current to follow. The sum of voltages across all the components is equal to the voltage across the cell or battery The size of current flowing in different parts of the circuit can be different. If one bulb breaks, all the others go out. They have the same current flowing in all parts of the circuit They have only one path for current to follow If you put more bulbs in they will stay bright

Ohm’s Law

Charles-Augustin de Coulomb André Marie Ampère (1736 – 1806) André Marie Ampère (1775 – 1836) George Simon Ohm (1789 – 1854) What is: a coulomb; an ampere; an ohm; and a volt? Alessandro Giuseppe Antonio Anastasio Volta 1745 - 1827

Charles-Augustin de Coulomb Explanations Charles-Augustin de Coulomb (1736 – 1806) a coulomb. You should LEARN that: The COULOMB is a unit of charge made up of a fixed Quantity (number) of electrons. The charge of one electron is: –1.6 x 10-19 C. More precisely: –1.602 176 487(40) × 10–19 C The ACTUAL quantity of electrons that makes up the coulomb is the inverse of the charge of one electron. (1.6 x 10-19)-1 = 6.2 x 1018 electrons. Or more precisely 6 241 509 629 152 650 000 electrons.

A = C s-1 Explanations André Marie Ampère an ampere. (1775 – 1836) an ampere. You should LEARN that: One ampere (A) describes the current flow of one unit of charge (C) passing a point in a circuit in one second (s). A = C s-1 an ohm. George Simon Ohm (1789 – 1854) You should LEARN that: The ohm is a measure of the resistance to the flow of current. The value of resistance determines how well a conductor conducts electricity. The smaller the number, the better the conductor. The unit of resistance is the ohm (W). Resistance is proportional to L & 1/A

Alessandro Giuseppe Antonio Anastasio Volta Explanations Alessandro Giuseppe Antonio Anastasio Volta 1745 - 1827 a volt. You should LEARN that: A volt is the gain or loss of one unit of energy by one unit of charge. A unit of energy is the joule (J) and a unit of charge is the coulomb (C). Example A fully charged 12 V battery has a potential rise (pr) of 12 V. This means that every unit of charge (C) has gained 12 J of energy since V = J C-1 A potential drop (pd) of 12 V across a resistor means that each unit of charge (C) has lost 12 J of energy since V = J C-1 This energy has been transformed into heat.