A short circuit occurs when current passes through a shortened path in the circuit, causing the current to become very large and the wires to heat up. An octopus connection is a fire hazard because it causes the current, voltage, and resistance to become very high. An ammeter is connected in series to measure current, while a voltmeter is connected in parallel. Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them.

1. NAT Review:
• 1. When does a short circuit occur?
• a. It occurs when the current passes through
a shortened path in the circuit
• b. It occurs when the current becomes very
large and the wires becomes very hot
• c. Both a and b
• d. None of the above

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2. Why is octopus connection fire hazard?
A. current becomes very high
B. voltage becomes very high
C. resistance becomes very high
D. All of the above
3. How is the ammeter connected to the circuit in
order to measure the current?
A. in parallel
B. in series
C. Both in parallel and series
D. In any way

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4. Ammeter is to series: _________is to parallel.
A. galvanometer
B. voltmeter
C. fuse
D. electric meter
5. What law states the electric force between two
charges?
A. Coulombs law
B. Newtons Law
C. Law of conservation of mass
D. Law of gravitation

4. OHM’S LAW
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The three basic electrical quantities are:
> electric current ( I ) in Ampere
> Voltage ( V ) in Volts
> Resistance ( R ) in ohm or Ω
How are these three related to one
another?
• Answer the Activity on Ohm’s Law.

5. • Questions:
• From table A what happens to current as the
voltage increases?
• Describe the graph of voltage against
current? What does the graph indicate?
• In table B describe the values of resistance
in each reading?
• What quantity seems to affect the current?
• Describe the graph of table B. What is the
relationship that exists in table B?
• How do you state Ohm’s Law?

6. • The relationship
between Voltage, Current and Resistance in any
DC electrical circuit was firstly discovered by the
German physicist Georg Ohm, (1787 1854). Georg Ohm found that, at a constant
temperature, the electrical current flowing
through a fixed linear resistance is directly
proportional to the voltage applied across
it, and also inversely proportional to the
resistance. This relationship between
the Voltage, Current and Resistance forms the
bases of Ohms Law and is shown below.

7. Ohms Law Relationship

8. Ohm’s Law Triangle

9. Application:
• Solve the given problems step by step:
• 1. How much current flows in an electric
fan having a resistance of 22 Ω when
connected across a 220 V line?
• Illustrate /draw the circuit on the board.
• Given:

10. 220 V
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22 Ω

11. • 2. An electric heater uses 5 A when 220 V
is applied to its terminal ,what is the
resistance in the circuit?