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Voltage, Current, Resistance, Ohm’s Law. 10.9, 10.10 Ohm’s Law questions handout. Electric Current (10.9). Shocks from electric circuits are very serious in comparison to shocks from static electricity. Every year people are injured and sometimes die from electrocution.
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Voltage, Current, Resistance, Ohm’s Law 10.9, 10.10 Ohm’s Law questions handout
Electric Current (10.9) • Shocks from electric circuits are very serious in comparison to shocks from static electricity. • Every year people are injured and sometimes die from electrocution. • Surprisingly small amounts of electric current are lethal.
Remember, electric current is a measure of the rate at which electric charges move past a given point in a circuit. • Unit for current is Ampere (A). • Symbol in the Ohm’s Law formula for current is (I).
Read p 314-315, Copy Fig 1. p 314 • How much current do you think someone experiences when they are electrocuted (death by the electric chair)? • Why is it dangerous to try to help someone who is experiencing an electric shock? Explain what you should do if you wish to help that person?
ELECTRIC POTENTIAL: VOLTAGE (V) • A volt is a measure of electrical pressure and is named after the Italian scientists Alessandro Volta. • The energy each electron has is called the electric potential. Electric potential is commonly referred to as voltage. • A Voltmeter is used to measure voltage. The symbol for this unit is V.
CURRENT (I) • Electric current is the quantity of electricity going by a point in a circuit. • Current (I) is measured with an ammeter. The unit used to measure electric current is the ampere, which is named after the French physicist A.M Ampere.
RESISTANCE (R) • The molecules of all types of conductors impede, or resist, the flow of electrons to some extent. • This ability to impede the flow of electrons in conductors is called electrical resistance (R).
RESISTANCE (2) • The resistance to the passage of electric current is measured with the ohmmeter. The unit is the ohm, named after the German scientist George Ohm. • INSULATORS oppose the flow of electric current and have a high resistance. • CONDUCTORS have a low resistance.
Factors that affect the resistance of wires: • The thickness of wires • The length of wire • The material of wire • The temperature of the wire
OHM’S LAW George Ohm figured out a basic law for electricity V= Volts (electrical potential) I= Amperes (current) R= Ohms (resistance) V = I x R I = V / R R = V / I
OHM’S LAW (2) • Current is directly proportional to voltage, therefore, increasing (↑) the voltage increases (↑) the current. • The current is inversely proportional to resistance; therefore, as resistance increases (↑), current decreases (↓).
Questions 1. What is the formula for Ohm’s Law? V = I x R 2. If a water heater has a voltage drop of 240V and a resistance of 12.8Ω, what is the current? I = V / R I = 240V / 12.8Ω I = 18.75A The water heater has a current of 18.75 amps.
2. If a coffee grinder has a current of 1.20A and resistance is 100Ω, what is the voltage? 3. If a food dehydrator has a voltage of 320V and has a current of 18.5A, what is the resistance? 4. If the current of a walkman is 4.7 A and the resistance of 26Ω, what is the voltage?