3 e electronics 091210
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Transcript of 3 e electronics 091210
Electricity
3E: Thursday 9th December
Experimental setup
1. Set up the circuit as shown2. Turn on the power supply and adjust the supply voltage to 6V3. Take readings of current, I (A), through, and the voltage, V (V) across the
resistor and record in a table in your workbook – use a ruler!4. Repeat this for several different values (6V down to 0V) of the voltage
and record both voltage and current through the resistor in your table of results
5. Plot a graph of your results (voltage, V (V) on y-axis; current, I (A) on x-axis) using a best fit line – use a ruler!
Battery Pack
A
VResistor
Analysing results:
I (A) V (V)
Voltage, V (V)
Current, I (A)
0V0A
Gradients
• How do we find a gradient of a graph in maths?
• Instead of y we have Voltage, V, instead of x we have Current, I
• If we have a straight line, the gradient is constant• Gradient, m = V/I = constant: RESISTANCE
Definition of Resistance• Electrical Resistance of an object is a measure of its opposition to the passage
of an electric current• Resistance is measured in Ohms (Ω)
Resistance = voltage / current
R=V/I V=IR I=V/R
George Simon Ohm
German Physicist
V
I R
Ohm’s Law questions
• V = IR
• Complete the questions on the handout
Resistors
• Resistors are simple components used to control the current and voltage in a circuit
Resistive heating
• For a given component, power P = IV where I is the current through that component and V is the voltage across that component
• Substituting from V=IR we get:P = I2R = V2/R = IV
Power is measured in Watts
Resistors in series
• If we join resistors in series we increase the resistance of the circuit. The current will decrease
• The total resistance in series is equal to the sum of the individual resistances:
Rs = R1 + R2 + R3
where Rs = equivalent series resistance
Resistors in parallel
• If we join components in parallel we decrease the resistance of the circuit. The current will increase.
• The combined resistance in parallel is calculated using the formula:
1/RP = 1/R1 + 1/R2 + 1/R3
where RP = equivalent parallel resistance