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Do now! Can you continue the questions from last lesson? Last lesson • Understand the term resistance • Recall and use: V =IR Resistance Measures how difficult it is for current to flow. Measured in Ohms (Ω) V Resistance = voltage/current A R = V/I Ohm’s Law • V = IR V I X ☺ R Can you copy this please? Let’s measure a resistance! Resistance of a lamp Vary the voltage and current using a variable resistor (rheostat). Plot a graph of resistance against current V Resistance = voltage/current A R = V/I Resistance of a lamp V(V) I(A) R(Ω) R(Ω) I(A) Resistance of a lamp • As the current in a lamp increases the electrons collide with the atoms in the wire making them vibrate (get hot). This vibration makes it harder for the electrons to travel in the wire and so the resistance increases. Today’s lesson • Understand the term power • Recall and use: P =VI Power The amount of energy used by a device per second, measured in Watts (Joules per second) A V Power = voltage x current P = VI Power The amount of energy used by a device per second, measured in Watts (Joules per second) A V ☺ Can you copy this please? Power = voltage x current P = VI Power of a lamp Measure the power of the lamp at it’s operating voltage. What is the electrical energy being turned into? A V Power = voltage x current P = VI Power of a lamp Since P = VI, and V = IR, P = I2R = V2/R V A Simple! Let’s try some questions! Homework • Due 18th November (Wednesday) • “Power” sheet • Finish “Resistance” questions