Electricity and Circuit

Types of Electricity Static Electricity – no motion of free charges Current Electricity – motion of free charges – Direct Current (DC) – Alternating Current (AC)

Electrical Circuits A circuit is a loop of wire with its ends connected to an energy source such as a battery. One end of the wire is connected to the positive terminal; the other end of the wire is connected to the negative terminal. The wire is connected in this way so a current can flow through it.

Series Circuits Resistors can be connected in series; that is, the current flows through them one after another.

Parallel Circuits A parallel circuit is rather like two or more series circuits connected to the same energy source. For example, here is a parallel circuit connected a battery and three resistors.

Series circuits have two disadvantages – If one component in a series circuit fails, then all of the components in the circuit fail because the circuit has been broken – The second disadvantage is that the more components there are, the greater the circuits resistance

Voltage Voltage (V) (also known as Potential Difference) can be thought of as the force pushing electric charges along a conductor – Measured in Volts (V) One volt is the electric potential difference between two points when one joule of work is done in moving one coulomb of charge between the points.

Resistance Resistance (R) is a measure of how difficult it is to push the charges along – Measured in Ohms (Ω) determines the amount of current flow = the ratio of potential difference to current

Resistance – “The pushing force” At each point in a circuit where the electrons need to be pushed, they use up their voltage. By the time the electricity gets back to the battery, the voltage is all used up and is 0 V

Equivalent Resistance

Current Electric Current (I) is the movement of electric charge in a conductor – Measured in Amps (A) 1 amp = 1 coulomb per second = 1 C/s

Current – “the number of moving electrons” In a series circuit the current is the same at every point in the circuit.

Ohm’s Law The ratio of potential difference to current is constant. If R = V/I is a constant value If R = V/I is a constant value for a given resistor, then that for a given resistor, then that resistor is said to obey Ohm’s Law. resistor is said to obey Ohm’s Law.

Voltmeter a device that measures electric potential difference, must be connected in parallel

Ammeter a device that measures current attached in series

Circuit Diagram Symbols

Practice Problem 1 Series, parallel, combination? Equivalent Resistance? Current?

Practice Problem 2 Series, parallel, or combination? Equivalent resistance? Current?

Practice Problem 3 Series, Parallel or combination? What is the equivalent resistance? What is the current?

Power Electric Power – rate of converting electric energy into other energy forms To calculate Power in a circuit, multiply current and the voltage: P = IV Power is measured in Watts

Practice Problems Practice Problem 1: The electric power of a lamp that carries 3A at 120 V is? Practice Problem 2: If a 1.2 A of current flow through a light bulb connected to a 120 V outlet, the power consumed is?