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Topic 2
ELECTRICITY WITHIN A CIRCUIT
Circuits
• Electric circuits
provide a
continuous
pathway.
Circuit Elements and Diagrams
Most complex circuits are made up of only
four basic elements.
• Source: The source of electric energy.
• Conductor: The wire through which
current flows.
• Load: Items along the circuit that convert
electricity into other forms of energy.
• Control: A switch or device that can turn
the circuit or devices along it on or off.
• .
Circuit Elements and Diagrams
• A battery is a combination of cells.
• You can use a switch to “open” or
“close” a circuit to control the flow of
current through it.
• A resistor is used to represent one of
many different loads.
Measuring Current
• Electric current is the amount of
charge that passes a point in a
conducting wire every second.
• The symbol for the current is I.
• Electric current is measured in
amperes (A) or milliamperes (mA).
Measuring Current
• An instrument used to measure very
weak electric current is called a
galvanometer. Larger currents are
measured with an ammeter of
milliammeter. The symbols for these
instruments are a circle with “G,” “A,” or
“mA” in the center, respectively.
Measuring Voltage
• The energy for pushing electrons
through comes from separated positive
and negative charges.
• In a battery, energy from chemical
reactions does the work of separating
the charges.
• All forms of energy are measured in
joules (J).
Measuring Voltage
• The energy of electrons in an electric
circuit is described by a standard unit
of charge instead of the total energy
of all of the changes.
Measuring Voltage
• Potential difference means the difference
in energy per unit of charge between one
point in the circuit and another point in the
circuit.
• Potential difference is commonly referred
to as voltage.
– The standard unit for potential difference is the
volt (V), named after Alessandro Volta (17451827), who built the first battery. Voltage is
measured with a voltmeter; the symbol for a
voltmeter is a circle with “V” at the centre.
Current and Voltage
• Electric current is equal throughout a
circuit.
• For the electric current to flow in a circuit,
the battery must be supplying energy &
there must be a continuous pathway for the
electric current to travel.
• Factors that affect the strength of an
electric current in a circuit include the
number of cells, voltage of the bulbs, type
& length of the conductor, and the
presence of loads.
Current and Voltage
• Batteries provide electrical energy.
• Loads use electrical energy.
• The energy provided to a circuit is very close to
the energy used.
• The voltage across individual loads adds up to a
voltage very similar to the voltage across the
entire load.
• Voltage is higher when loads are removed
because there is less resistance within the
circuit.
Rivers of Electricity
• The load of an electrical circuit is comparable
to a water wheel in a water system:
– A switch is comparable to a valve
– An electrical current is comparable to a flow rate
– Voltage is comparable to pressure
– A battery is comparable to a pump
– A conductor (wire) is comparable to a pipe