Famous Physicists

Alessandro Volta (1745 –1827)

Alessandro Volta was an Italian physicist. He invented electric battery in 1800.

Georg Simon Ohm (1789 – 1854)

Georg Simon Ohm was a German physicist. Ohm determined that the potential difference (voltage) applied across a conductor is directly proportional to electric current. Now this relationship is known as Ohm's law.

André-Marie Ampère (1775 –1836)

André-Marie Ampère was a French physicist who founded the science of electrodynamics and electromagnetism. He demonstrated that electric currents produce magnetic fields. The unit of measurement of electric current, the ampere, is named after him.

Current, I

Text 2

Connecting an ammeter in series

· Current is the rate of flow of charge.

· Current is not used up, what flows into a component must flow out.

· We say current through a component.

· Current is measured in amps (amperes), A.

· Current is measured with an ammeter, connected in series.
To connect in series you must break the circuit and connect the ammeter in the gap.

· The symbol I is used for current in equations.

The need to break the circuit to connect in series means that ammeters are difficult to use on soldered circuits. Most testing in electronics is done with voltmeters which can be easily connected without disturbing circuits.

1A (1 amp) is quite a large current for electronics, so mA (milliamps) are often used.

m (milli) means "thousandth": 1mA = 0.001A, or 1000mA = 1A

Voltage and Current for components in Series

Voltages add up for components connected in series.
Currents are the same through all components connected in series.

In this circuit the 4V across the resistor and the 2V across the LED add up to the battery voltage: 2V + 4V = 6V.

The current through all parts (battery, resistor and LED) is 20mA.

Voltage, V

Text 3

Connecting a voltmeter in parallel

· Voltage is a measure of the energy carried by the charge. Voltage is sometimes called the potential difference.

· Voltage is supplied by the battery (or power supply).

· Voltage is used up in components, but not in wires, and we say voltage across a component.

· Voltage is measured in volts, V.

· Voltage is measured with a voltmeter, connected in parallel.

· The symbol V is used for voltage in equations.

Voltage at a point and 0V (zero volts)

In electronics voltage at a point is the voltage difference between that point and a reference point of 0V (zero volts).

Zero volts could be any point in the circuit, but it is normally the negative terminal of the battery or power supply. Circuit diagrams are often labelled with 0V as a reminder.

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