Download Electricity and Circuit

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
0V
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
• for a given resistor, then that
• 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?