What is resistance And how do we calculate
- Slides: 18
What is resistance And how do we calculate it
Resistance simulation 3 of 31 © Boardworks Ltd 2011
All components have resistance. What happens if you increase the resistance in a circuit? The current in the circuit decreases 4 of 31 © Boardworks Ltd 2011
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What happens when the switch is closed? 6 of 31 © Boardworks Ltd 2011
Resistance is the opposition that an electrical device has to the flow of electrical current. All devices have some resistance. A resistor is a device that has a particular resistance. a resistor circuit symbol for a resistor
A variable resistor is a component whose resistance you can change. By increasing the resistance, you can decrease the current in the circuit. Symbol for a variable resistor Can you think of a practical application using a variable resistor?
Resistance equation resistance = potential difference current Where: potential difference is in volts (V) current is in amperes (A) resistance is in ohms (Ω) R=V÷I
Also: potential difference = current x resistance and: current = potential difference resistance potential difference V current I resistance R
Measuring Resistance The resistance of a component can be found by measuring the current through, and potential difference across, the component. Circuit used for measuring the resistance of an indicator lamp
Question 1 Calculate the resistance of a lamp if a potential difference of 12 V causes a current of 3 A to flow through the lamp. resistance = potential difference current = 12 V / 3 A resistance = 4 ohms (4Ω)
Question 2 Calculate the resistance of a heater if a potential difference of 230 V causes a current of 200 m. A to flow through the heater. resistance = potential difference current = 230 V / 200 m. A = 230 V / 0. 200 A resistance = 1150 Ω
Question 3 Calculate the potential difference across a resistance of 40Ω when a current of 5 A is flowing. potential difference = current x resistance = 5 A x 40Ω potential difference = 200 V
Complete: Answers potential difference 20 V current resistance 4 A 5Ω 200 V 5 A 40 Ω 300 V 0. 20 6 A 50 Ω 8 V 500 m. A 16 Ω 3 k. V 20 A 150 Ω 120 V 4 m. A 30 kΩ
What affects resistance? The resistance of a wire depends on several factors: l material l thickness l length l temperature What experiments could be used to test how length and thickness affect resistance? 16 of 31 © Boardworks Ltd 2011
Investigating a factor that affects the resistance of a wire. 17 of 31 © Boardworks Ltd 2011
Some materials, when cooled down sufficiently become superconductors. This means that they effectively have no resistance and can be used to make very strong electromagnets. https: //www. youtube. com/watch? v=h. TT 6 nkt. JQBE Some materials are neither conductors nor insulators but somewhere in between. These materials are called semiconductors and when energy is given to them they can become conductors. 18 of 31 © Boardworks Ltd 2011