1. OHM’s Law SNC 1D0 Monday November 29 Electrical Resistance
Short Circuit
Ohm’s Law
GUESS Method
Practice Questions

2. 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)

3. 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)

4. 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 = I x R V = electric potential
(voltage drop) (V)
I = electric current, (A) R = electrical resistance (Ω)

5. Rearranging the Equation
V = I x R

6. 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

7. 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 A is flowing through it.

8. Practice – use the GUESS method
1. Copy and complete the table:
Resistance
()
Voltage
(v)
Current
(A) 25 30
2.5 72
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?

9. Classwork/Homework
Answer questions 3, 5, 6, 7 from page (Ohm`s law)