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Transcript
Grade 9 Academic Science – Electricity
Resistance and Ohm’s Law
Section 13.7
Electrical resistance is the opposition to the movement of electrons as they flow through a circuit.
An ohmmeter is used to measure the resistance. It is placed in series across a load.
A resistor is an electrical device that reduces the current in a circuit. Resistors have may uses. Light
weight carbon resistor are used in electronics, variable resistors are used as dimmer switches, and
ceramic resistors are used in big circuits (high voltage lines – metal electrical towers).
Current, Voltage and Resistance – Ohm’s Law
Activity: Test the relationship between current and voltage with two different resistors
Potential
Difference
(V)
Current
At Resistor A
(A)
Current
at Resistor B
(A)
0
1
2
3
4
5
Ohm’s Law states that as the potential difference increases, so does the current. When graphed there is
a straight line relationship between voltage and current. The slope of a V / I graph is the
resistance. The relationship among current, potential difference and resistance can be written
mathematically as the equation I = V / R
Sample
A load has 1.2 A of current running through it. The voltage across the load is 6.0 V. Calculate the
resistance. Use Ohm’s Law…re-arrange the formula to solve for resistance.
Practice / Homework -- Try the practice word problems on Page 568, Questions 1-9, Page 570