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SNC 1D0
Monday November 29
OHM’s Law
-Electrical Resistance
-Short Circuit
-Ohm’s Law
-GUESS Method
-Practice Questions
Electrical Resistance – the ability to impede (obstruct)
the flow of electrons.
Symbol = R
Unit = Ohm (Ω)
When electrons flow through a resistor, it causes a
loss of electric potential (voltage drop)
Short Circuit
• Electrons are lazy, they will take the path of least
resistance
• Electrons are allowed to flow through the circuit
without a load, they return to the cell without
losing voltage
• May become hot and cause fire
(i.e. starting a fire with a battery)
Ohm’s Law – the potential difference between two
points on a conductor is proportional (directly
related) to the electric current flowing through the
conductor.
V=IxR
V = electric potential
(voltage drop) (V)
I = electric current, (A)
R = electrical resistance (Ω)
Rearranging the Equation
V=IxR
GUESS Method
Given – write down the information given in the
question
Unknown – write down the information you need to
find
Equation – write down the equation you will use to
solve the question
Solution – substitute and solve your solution
Statement – make a therefore statement
Question: What is the voltage drop across the
tungsten filament in a 100-W light bulb? The
resistance of the filament is 144  and a current of
0.833 A is flowing through it.
Practice – use the GUESS method
1. Copy and complete the table:
Resistance
()
25
72
Voltage
(v)
30
Current
(A)
30
2.5
0.25
2. If the current through a 25  resistor is 0.2 A, what is the voltage drop?
3. The voltage drop across a 18  resistor is 6 V. Find the current through the resistor.
4. An electric clothes dryer is connected to a 230 V source of electric potential. If the
dryer has a resistance of 9.2 , calculate the current that it draws.
5. An electric kettle is connected to a 120-V outlet and has a resistance of 9.6 ohms.
What is the current required to operate the kettle?
Classwork/Homework
1. Answer questions 3, 5, 6, 7 from page 458- 464 (Ohm`s
law)