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# Electric Current Save Print Edit
Electric Current
• Astrophysics • Atoms and Radioactivity • Electricity • Energy Physics • Engineering Physics • Fields in Physics • Force • Further Mechanics and Thermal Physics • Magnetism • Measurements • Mechanics and Materials • Medical Physics • Nuclear Physics • Particle Model of Matter • Physical Quantities and Units • Physics of Motion • Radiation • Space Physics • Turning Points in Physics • Waves Physics Electricity is a form of energy. It is the phenomenon that describes the flow of charged particles (particularly electrons) from one place to another. Everything in the world is made up of atoms. Every atom is composed of a nucleus surrounded by negatively charged electrons. The nucleus contains particles called neutrons (which have no charge) and protons (which have a positive charge). The number of protons and electrons is the same in a stable atom to balance the overall neutral charge.

In conductors (e.g., metals like copper or silver), the movement of electrons known as free electrons is responsible for moving the charge. The moving charge is what we call an electric current.

The phenomenon of electricity and its applications are studied in more detail in the field of electrical engineering.

## Defining electric current

We can define the electric current as the amount of charge that moves during a specific time period. The formula for calculating electrical current and the units used are as follows:

• The SI base unit for electric current is the amperes (A).
• Current (I) is measured in amperes (A).
• Q is measured in coulombs (C).
• Time (t) is measured in seconds (s).
• Charge, current, and time are related to each other as Q = I ⋅ t.
• Change in charge is denoted as ΔQ.
• Similarly, the change in time is denoted as Δt.

Another interesting point is that electrical current produces a magnetic field, while a magnetic field can also produce an electrical current.

## Batch variation

When two charged objects are connected using a conductive wire, a charge flows through them, producing a current. The current flows because the charge difference causes a voltage difference. Figure 1. Flow of charge in a conductor. Source: StudySmarter.

The equation for current flow, therefore, is: ### Conventional current flow

In a circuit, current is the flow of electrons across the circuit. Electrons, which are negatively charged, move away from the negatively charged terminal and towards the positively charged terminal, following the basic rule that like charges repel each other while opposite charges attract each other.

Conventional current is described as the flow of positive charge from the sources positive terminal to its negative terminal. This is opposite to the flow of electrons, as it was stated before the direction of current was understood. Figure 2. Conventional flow vs electron flow. Source: StudySmarter.

An important point to make is that the flow of current has a direction and magnitude given in amperes. However, it is not a vector quantity.

### How to measure current

Current can be measured using a device called an ammeter. Ammeters should always be connected in series with the part of the circuit where you wish to measure the current, as shown in the figure below.

This is because current has to flow through the ammeter in order for it to read the value. The ideal internal resistance of an ammeter is zero in order to avoid any voltage being on the ammeter because it can affect the circuit. Figure 3. Arrangement to measure current using Ammeter - StudySmarter Originals

Q: In which of the options below does 8 mA of current pass through the electrical circuit?

A. When a charge of 4C passes in 500s.

B. When a charge of 8C passes in 100s.

C. When a charge of 1C passes in 8s.

Solution. Using the equation: I = 4/500 = 8 x 10-3 = 8 mA

I = 8/100 = 80 x 10-3 = 80 mA

I = 1/8 = 125 x 10-3 = 125 mA

Option A is correct: 8 mA of current will pass through the circuit.

## Quantisation of charge

The charge on the charge carriers is quantised, which can be defined as follows:

A single proton has a positive charge, and a single electron has a negative charge. This positive and negative charge has a fixed minimum magnitude and always occurs in multiples of that magnitude.

Therefore, the quantity of charge may be quantised based on the number of protons or electrons present.

This means that a charge on any particle is a multiple of the magnitude of the charge of the electron. For example, the charge of an electron is -1.60 × 10 ^ -19 C, and the charge of a proton, by comparison, is 1.60 × 10 ^ -19 C. We can represent the charge of any particle as a multiple of this.

## Calculating current in a current-carrying conductor

In a current-carrying conductor, a current is generated when the charge carriers move around freely. The charge on the charge carriers can either be positive or negative, and the current is considered to travel in one direction across the conductor. The current in a conductor has several characteristics:

• The charge carriers are mostly free electrons.
• Although the current flows in a particular direction in each conductor, the charge carriers move in opposite directions with a drift speed v.
• The first image in Figure 2 has positive charge carriers. Here, drift speed and charge carriers move in the same direction. The second image has negative charge carriers, and drift speed and charge carriers move in the opposite direction.
• The charge carriers drift speed is the average speed at which they travel through the conductor.
• The current in a current-carrying conductor can be mathematically expressed as: Where A is the area of the cross-section, in units of area.n is number density (the number of charge carriers per m^3).v is drift velocity in m/s.q is the charge in Coulombs.I is the current in Amperes.

## Electric Current - Key takeaways

• Electricity is a form of energy. It is the phenomenon that describes the flow of charged particles (particularly electrons) from one place to another.
• The SI base unit of electric current is amperes (A).
• Conventional current is described as the flow of positive charge from the cell’s positive terminal to its negative terminal.
• The charge on the charge carriers is quantised.

Electric current is measured in Amperes (A) or amps.

Electric current is defined as the rate of flow of charge carriers.

An electric current always produces a magnetic field.

A magnet’s characteristics are utilised to generate electricity. Electrons are pulled and pushed by moving magnetic fields. Electrons in metals like copper and aluminium are scattered throughout. When you move a magnet around a coil of wire, or a coil of wire around a magnet, the electrons in the wire are pushed out and an electrical current is created.

Electric current is a scalar quantity. Any physical quantity is termed as a vector if it has magnitude, direction and also follows vector laws of addition. Though electric current has magnitude and direction, it does not follow the vector laws of addition. Hence electric current is a scalar quantity.

## Final Electric Current Quiz

Question

What is electricity?

Electricity is a form of energy.

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Question

How is electricity conducted?

By moving charge from one place to another.

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Question

What is the SI unit of electric current?

The SI unit of electric current is the Ampere (A) or amps.

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Question

How are charge (Q), current (I), and time (t) related to each other mathematically?

Q=I*t

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Question

Why is the direction different between conventional current and electron flow?

Conventional current is opposite to the flow of electrons because it was described before the direction of current was understood.

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What device do we use to measure electric current?

An ammeter.

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How should ammeters be connected to measure current?

In series.

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Question

How is charge quantised?

Positive and negative charges have a fixed minimum magnitude and always occur in multiples of that magnitude.

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Question

What is the drift speed of a charge carrier?

A charge carrier’s drift speed is the average speed at which it travels through the conductor.

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Question

In which of the options below does 2 mA of current pass through a wire?

When a charge of 4C passes in 2000s.

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Question

In which of the options below does 3 mA of current pass through a wire?

When a charge of 3C passes in 1000s.

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Question

A charge of 10 Coulombs passes through a wire, producing a current of 1 ampere. Calculate how long this would take, using the charge, current, and time relationship.

10 seconds.

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Question

A charge of 4 Coulombs passes through a wire, producing a current of 2 amperes. How long does this take? Use the charge, current, and time relationship.

2 seconds.

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What charge do electrons have, positive or negative?

They have a negative charge.

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What charge do protons have, positive or negative?

They have a positive charge.

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What are the two main measuring devices in electric circuits?

Voltmeters and ammeters.

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Question

The voltage value at a ground point is what?

Zero.

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Question

What is the symbol for electric current?

I

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Question

What is the main use of a switch in electric circuits?

To stop and start the current flow.

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Question

Ideally, how much resistance does a diode show when the current is flowing from its anode to its cathode?

A resistance of zero.

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In reality, what happens if the current flowing through a diode’s anode to the cathode can’t reach its threshold level?

The current can't flow through.

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What is the voltage difference between a bipolar junction transistor’s base and emitter terminals?

0.7 volts.

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What is the name of the positive pole of a component?

The anode.

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What is the name of the negative pole of a component?

The cathode.

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Ideally, what resistance value does a diode show when the current is trying to flow from its cathode to its anode?

The resistance value of the diode should be infinite.

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Question

What is the equation for power in electricity?

P = V * I

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What is the equation for energy in electricity?

E = P * t

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Question

What decides the direction of the loop when applying Kirchhoff's second law?

You can decide the direction of the loop.

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Question

When applying Kirchhoff's second law, if the loop's direction goes through the positive pole first, which value will get the voltage of that component?

Positive.

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Question

When applying Kirchhoff's second law, does the direction of the loop affect the result?

No, the direction of the loop does not affect the result.

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Question

What determines the poles of a component?

The way the current enters the component.

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When applying Kirchhoff's second law, if the loop's direction goes through the negative pole first, which value will get the voltage of that component?

Negative.

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Question

When calculating the algebraic sum of the currents in a junction, in which order do we take the values of the currents going in and the currents going out?

Negative and positive.

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Question

Kirchhoff's second law states that in any closed loop in a circuit, the algebraic sum of the voltages is equal to what?

The algebraic sum of the voltages is equal to zero.

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Question

Energy is conserved in electric circuits. True or false?

True. Energy is conserved in electric circuits because of the law of conservation of energy.

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Question

Electrical energy is derived from the movement of electrons. True or false?

True, electrical energy is derived from the movement of electrons.

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Question

Which of the following is not one of the areas that voltage dividers are used in?

Current measurement.

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Question

Are voltage dividers used on multimeters?

Yes, voltage dividers are used on multimeters.

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Question

Which output ratio should be used to transform 10 volts into 2.5 volts?

2.5/10

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Can voltage dividers be used to optimise electronic equipment?

Yes, voltage dividers can be used to optimise electronic equipment.

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Question

Considering Ohm’s law, if the current value is constant, what is the relation between the voltage and the resistance?

They are directly proportional.

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Can voltage dividers be used as signal attenuators?

Yes, voltage dividers can be used as signal attenuators.

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When do voltmeters need voltage dividers to measure the value of the voltage?

When the voltage value is too big.

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After you have measured an amount of voltage that is applied through a voltage divider, which factor should it be multiplied/divided by to get the right result?

The factor that the input voltage was lowered by in the first place.

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Can a microcontroller read the resistance value of a sensor using voltage dividers?

Yes, a microcontroller can read the resistance value of a sensor using voltage dividers.

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Question

What are logic level shifters used for?

To connect two logic circuits.

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What happens when you don’t use a voltage divider when connecting two logic circuits that operate at different voltages?

The circuits will be damaged.

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Question

The output voltage of a voltage divider can be found from the resistance value of the output component divided by the total series resistance and multiplied by the voltage value of the source. True or false?

True.

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Question

Can you take multiple output voltages out of a voltage divider circuit with more than two resistors?

Yes, you can take multiple output voltages out of a voltage divider circuit with more than two resistors.

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Question

A battery has an emf of 0.45V. The current flowing through the battery is 0.07A and the load resistance is 1.3Ω. Find the internal resistance of the battery.

5.13Ω

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