Calculate the Resistance when… A kettle operates with 230V and 13A. Motor runs on mains voltage with a 3A current. A length of copper wire has a p.d. of 1mV and a current of 3A. EXT 1: A TV operates with a power of 2.5KW and on mains voltage. EXT 2: A lawnmower operates with a current of 12A and a power of 1.5KW.

Learning Objectives By the end of this lesson you should be able to… List some factors affecting resistance in different materials. Explain the effect of temperature, length, material and cross sectional area on resistance. Practise building test circuits and concluding on your own.

Factors Affecting Resistance Learning Objectives By the end of this lesson you should... List some factors affecting resistance in different materials. Explain the effect of temperature, length, material and cross sectional area on resistance. Practise building test circuits and concluding on your own. Factors Affecting Resistance Temperature – In metals resistance increases with temperature. Material – Some materials offer a higher resistance than others, e.g. insulators or conductors. Length – Longer wire, of constant area and material will offer a higher resistance than shorter wire. Cross-sectional area – Thicker wire will offer a different resistance to thinner wire of the same length and material.

Factors Affecting Resistance Learning Objectives By the end of this lesson you should... List some factors affecting resistance in different materials. Explain the effect of temperature, length, material and cross sectional area on resistance. Practise building test circuits and concluding on your own. Factors Affecting Resistance Temperature There is a heating effect when a _______ flows through a conductor. This occurs because the flowing electrons _______ with atoms within the conductor as the pass. The electrons lose _______ with is gained by the atoms causing them to ________ faster. These additional ________ mean the material has a ________ temperature.

Factors Affecting Resistance Learning Objectives By the end of this lesson you should... List some factors affecting resistance in different materials. Explain the effect of temperature, length, material and cross sectional area on resistance. Practise building test circuits and concluding on your own. Factors Affecting Resistance Material In order to conduct electricity materials need to have ______ _________ (charge carriers). Some materials have a high density of charge carrying particles, these we call _________. Some materials have essentially no charge carriers, these we call _______.

Factors Affecting Resistance Learning Objectives By the end of this lesson you should... List some factors affecting resistance in different materials. Explain the effect of temperature, length, material and cross sectional area on resistance. Practise building test circuits and concluding on your own. Factors Affecting Resistance Length Your experiment today – build a standard test circuit and change the length (of copper wire) through which the current is flowing. You need to deduce the nature of the relationship, e.g; when I double the length the resistance will…………….. If I use the half the length the resistance will ……………….

Factors Affecting Resistance Learning Objectives By the end of this lesson you should... List some factors affecting resistance in different materials. Explain the effect of temperature, length, material and cross sectional area on resistance. Practise building test circuits and concluding on your own. Factors Affecting Resistance Cross sectional Area Your second experiment today – build a standard test circuit with a second thickness of wire, you can then change the length through which the current is flowing. You need to deduce the nature of the relationship, e.g; when I double the length the resistance will…………….. If I use the half the length the resistance will ……………….

Factors Affecting Resistance Learning Objectives By the end of this lesson you should... List some factors affecting resistance in different materials. Explain the effect of temperature, length, material and cross sectional area on resistance. Practise building test circuits and concluding on your own. Factors Affecting Resistance Things to think about; Building a standard test circuit, what components should go where and what would an appropriate value for p.d. be? You need a table of results drawn in your book You will need 1 graph WITH ALL NECESSARY PARTS (you can plot both experiments on one axis – if you are careful). You need to conclude your experiment – what is the relationship and why – use P184 in the Pople books to help. You need to evaluate your experiment, how were errors minimised and how well did that work? Finished? What would your graph look like if you had plotted radius instead of cross sectional area? Read P192/193 about electricity in home and answer Q’s.