Electrical Circuit

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Electrical Current

Electric current is a flow of electrons.

In order for an electric current to flow there needs to be a complete circuit. A basic electric circuit consists of a metallic wire connected to a electrical cell for example a lamp. The metallic wire contains a large number of free electrons that can easily move from atom to atom. It is the movement of these free electrons that give rise to the current.

Electric current is measured in amps. (A)

1 amp is a set number of electrons passing a certain point in one second. Approximately 6 million... million....million...million...million...

As the charge on electrons is tiny the unit of charge used is the coulomb (c) 1 coulomb is equal tot the charge of 6 million.... million..... million..... million..... million....million... electrons. Therefore when a current in a circuit is 1 ampere the flow of charge is 1 coulomb per second.

Electric current is measured by an Ammeter.

Electrical current flows through a component such as a lamp or ammeter. Electrons are not used up but instead continue to flow around in a continuous loop. The battery supplies the energy source for the electrons to move. These transfer or lose electrons when passing through components such as a lamps in the form of heat and light but doesn't get used up itself. Therefore in a series circuit the electrical current is the same in all parts of the circuit.

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Potential Difference

In a circuit the cell (Battery) pushes the electrons around the circuit. It does this by transferring chemical energy from the materials in the cell to electrical potenital energy to the electrons.

When electrons pass through a lamp in a circuit they give up (lose) some of the electrical potential energy to the thin wires in the lamp in the form of heat and light. Therefore across the lamp there is an electrical energy difference. The electrons entering the lamp have a higher electrical energy than the electrons leaving the lamp. This difference in electrical potential energy across the lamp is called Potential difference

Potential Difference is measured in volts (V)

Potential Difference is measured by a voltmeter

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Resistance

Electric Current is the flow of electrons. As these electrons flow around a circuit they bump into the atoms in the conducting wire and electrical components. These constant collisions make it difficult for the current to flow. (Resist the electrical current)

Resistance is the property of an object or substance resisting the flow of electrons.

Resistance is measured in Ohms

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Convectional Current & Electron Flow

Electric current is the flow of electrons from the negative terminal to the positive terminal of the cell. This is because electrons are negatively charged resulting in the electrons moving away from the negative terminal and attracting towards the positive terminal.

Current flow from the positive to the negative is called Convectional Current. The convectional current flows in the opposite direction to the electron flow.

Series Circuits

1.Electric Current: The electrical current through each component is the same as all the current has to pass through all of the components in the circuit in order for it to work.

All the current has to flow through everything in the circuit.

The electrical current through each component is the same.

2.Potenital difference: The potential difference across each component add up to the potential difference across the battery. This is because the energy transferred from the battery to the the electrons must be equal to the amount of energy transferred by the electrons to the components. The potential difference provided by cells connected in series is the sum of the potential difference of each cell.

The potential difference across each component adds up to the potential difference across the battery.

V=V1+V2

The potential difference provided by cells connected in series is the sum of the potential difference of each cell.

3. Resistance: The total resistance across the component in series is equal to the sum of each resistance across the components. The potential difference is largest across the component with the greatest resistance as more energy is transferred by electrons to overcome the resistance.

The total resistance across the components in series is equal to the sum of each resistance across the components.

R= R1+R2

Parallel Circuits

1. Electrical current: The total current through the whole circuit is the sum of the current through each electrical component. The current in a parallel circuit branches out after leaving the battery and recombines before entering back in.

The total current through the whole circuit is the sum of the current through each electrical component.

The electrical current in the main circuit is the sum of the currents in the separate branches.

2A= 1A + 1A

2. The potential difference across each component is the same.

3. The combined resistance across the components in parallel is less than either of the separate resistance across the components.

The combined resistance across the components in parallel is less than either of the separate resistance across the components.

1/R= 1/R1 + 1/R2

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Ohm's Law

The current flowing through a metallic conductor held at constant temperature is directly proportional to the potential difference between the ends.

If the current doubles the potential difference doubles.

Or if the current triples the potential difference triples.

Ohms Law can be stated for the current through a resistor as:

The current flowing through a resistor held at constant temperature is directly proportional to the potential difference across the resistor.

Potential difference or Voltage (v) = Current (I) x Resistance (R)

v=I x R

Example

In the circuit below the voltmeter reading around the lamp is 3V and the ammeter reads 2A of electrical current. What is the resistance across the lamp?

Potential Difference across the lamp= V= 3V

Electrical Current through the lamp= I = 2A

Electrical resistance across the lamp= R=?

R= V/I

R=3/ 2

R= 1.5 Ohms

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