Electrical Potential (Voltage) Answers (Page 303)

1. a) Why is it necessary for the electrons to move continuously around the circuit?

b) From which terminal do the electric charges flow into the circuit? Explain.

2. a) Define the term “electrical potential”?

b) State the SI unit and the name the symbol used for electrical potential

3. Why is it possible to measure an electrical potential across the terminals of a dry cell, even if the electrons are not flowing into the circuit?

Measuring Electricity

Electric Potential – the electrical energy that an electron possesses.

Electric current is a measure of the rate at which the electric charges move past a given point in a circuit. Ampere (A) is the S.I. unit used to measure electric current.

Ex: In a 100 w light bulb only 1A of current flows through it.

Voltage – electric potential

Volts (V) – the S.I. unit used to measure electric potential.

Voltage Drop – a measure of the energy each electron gives up as it moves through a circuit. (Commonly used for potential difference.)

Electrical ResistanceElectrical Resistance

Resistance – is the ability to hold back the flow of electrons in a conductor. The molecules found in every type of conductor resists the flow of electrons to some extent.

Resistors – are electrical devices that are used in circuits that are designed to resist the flow of electricity. The symbol for electrical resistance is “R” and the S.I. unit is the Ohm ().

Ex: the resistance of a 100 W light bulb is about 144 .

When electrons flow through a conductor the electrical resistance causes a loss of electric potential (voltage). There is a “difference” in the amount of electric potential after the electrons have flowed through the conductor. This difference is referred to as the potential difference.

Ohm’s LawOhm’s Law

Ohm’s Law:Ohm’s Law: The potential difference between two points on a conductor is proportional (directly related) to the electric current flowing through the conductor.

Potential = Electric Current x Electrical Resistance Difference (Voltage Drop)

V = I x RV = I x R

Potential difference (V) is measured in volts (V)

Electric Current (I) is measured in ampere (A)

Resistance (R) is measured in ohms ()

Ohm’s Law Questions

Sample Problems:

1. What is the voltage drop across the tungsten filament in a 100 watt light bulb? The resistance of the filament is 144 ohms and a current of 0.833 amperes is flowing through it.

I = 0.833 AR = 144 OHMSV = ? V

V = I X RV = (0.833A)(144Ω)V = 120 VThe voltage drop across a 100 watt light bulb is

120 V.

2. An electric toaster is connected to a 120 V outlet in the kitchen. If the heating element in the toaster has a resistance of 14 Ohms. Calculate the current flowing through it.

V = 120 V I = ? A R = 14 OHMS

V = I X R120 V = I X (14 Ω)120V = I14 ΩI = 8.6 AThe current flowing through the toaster is 8.6

A.