1. The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan Electric Circuits and Resistance M.D.

2. PDST Resources for Leaving Certificate Physics 2 A + - conventional current VVoltage ‘pushes’ the current resistance restricts the currentR I is the current lamp switch actual current Electric Circuits

3. PDST Resources for Leaving Certificate Physics 3 Resistance slows down the movement of electrons… …and therefore reduces the current The resistance of an object is the ratio of the voltage applied across its ends to the current which flows through it. Resistance

4. PDST Resources for Leaving Certificate Physics 4 Resistance and Temperature  Heat source R /  T / o C metal  Heat source R /  T / o C Semiconductor

5. PDST Resources for Leaving Certificate Physics 5 Resistors in Series and Parallel Series R1R1 R2R2 R3R3 Total Resistance: Parallel Total Resistance: R1R1 R2R2 R3R3

6. PDST Resources for Leaving Certificate Physics 6 Resistance and Resistivity Which has higher resistance? l A (= π r 2 ) plastic Resistivity, ρ

7. PDST Resources for Leaving Certificate Physics 7 2005, Q.9

8. PDST Resources for Leaving Certificate Physics 8 In the circuit diagram, the resistance of the thermistor (a semiconductor) at room temperature is 500 Ω. At room temperature, calculate (i) the total resistance of the circuit; (ii) the current flowing through the 750 Ω resistor. (20) 6V

9. PDST Resources for Leaving Certificate Physics 9 6V RpRp In the circuit diagram, the resistance of the thermistor (a semiconductor) at room temperature is 500 Ω. At room temperature, calculate (i) the total resistance of the circuit; (ii) the current flowing through the 750 Ω resistor. (20)

10. PDST Resources for Leaving Certificate Physics 10 6V 500 750 0.01 Resistances: 500:750 2:3 currents: 3:2 In the circuit diagram, the resistance of the thermistor (a semiconductor) at room temperature is 500 Ω. At room temperature, calculate (i) the total resistance of the circuit; (ii) the current flowing through the 750 Ω resistor. (20)

11. PDST Resources for Leaving Certificate Physics 11 As the temperature of the room increases, the resistance of the thermistor decreases. Explain why the potential at A increases (7) 6V Marking Scheme: The resistance (R) of thermistor (and 750 Ω combination) decreases (3) the potential drop (V=IR) across the thermistor and 750 Ω combination also therefore decreases (2) and the potential at A increases (2)