Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Electric Current

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Electric Current

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.

Current Electricity. Flow charge conventional. StudySmarterFigure 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.

Current Electricity. Current flow. StudySmarterFigure 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.

Current Electricity ammeter measuring current StudySmarterFigure 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.

Frequently Asked Questions about Electric Current

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?

Show answer

Answer

Electricity is a form of energy.

Show question

Question

How is electricity conducted?

Show answer

Answer

By moving charge from one place to another.

Show question

Question

What is the SI unit of electric current?

Show answer

Answer

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

Show question

Question

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

Show answer

Answer

Q=I*t

Show question

Question

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

Show answer

Answer

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

Show question

Question

What device do we use to measure electric current?

Show answer

Answer

An ammeter.

Show question

Question

How should ammeters be connected to measure current?

Show answer

Answer

In series.

Show question

Question

How is charge quantised?

Show answer

Answer

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

Show question

Question

What is the drift speed of a charge carrier?

Show answer

Answer

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

Show question

Question

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




Show answer

Answer

When a charge of 4C passes in 2000s.

Show question

Question

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


Show answer

Answer

When a charge of 3C passes in 1000s.

Show question

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.

Show answer

Answer

10 seconds.

Show question

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.

Show answer

Answer

2 seconds.

Show question

Question

What charge do electrons have, positive or negative?

Show answer

Answer

 They have a negative charge.

Show question

Question

What charge do protons have, positive or negative?

Show answer

Answer

They have a positive charge.

Show question

Question

What are the two main measuring devices in electric circuits?

Show answer

Answer

Voltmeters and ammeters.

Show question

Question

The voltage value at a ground point is what?


Show answer

Answer

Zero.

Show question

Question

What is the symbol for electric current?


Show answer

Answer

I

Show question

Question

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


Show answer

Answer

To stop and start the current flow.

Show question

Question

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


Show answer

Answer

A resistance of zero.

Show question

Question

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


Show answer

Answer

The current can't flow through.

Show question

Question

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


Show answer

Answer

0.7 volts.

Show question

Question

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


Show answer

Answer

The anode.

Show question

Question

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


Show answer

Answer

The cathode.

Show question

Question

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


Show answer

Answer

The resistance value of the diode should be infinite.

Show question

Question

What is the equation for power in electricity?

Show answer

Answer

P = V * I

Show question

Question

What is the equation for energy in electricity?


Show answer

Answer

 E = P * t

Show question

Question

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


Show answer

Answer

You can decide the direction of the loop.

Show question

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?


Show answer

Answer

Positive.

Show question

Question

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


Show answer

Answer

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

Show question

Question

What determines the poles of a component?

Show answer

Answer

The way the current enters the component.

Show question

Question

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?


Show answer

Answer

Negative.

Show question

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?


Show answer

Answer

Negative and positive.

Show question

Question

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


Show answer

Answer

The algebraic sum of the voltages is equal to zero.

Show question

Question

Energy is conserved in electric circuits. True or false?


Show answer

Answer

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

Show question

Question

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


Show answer

Answer

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

Show question

Question

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


Show answer

Answer

Current measurement.

Show question

Question

Are voltage dividers used on multimeters?


Show answer

Answer

Yes, voltage dividers are used on multimeters.

Show question

Question

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


Show answer

Answer

2.5/10

Show question

Question

Can voltage dividers be used to optimise electronic equipment?


Show answer

Answer

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

Show question

Question

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


Show answer

Answer

They are directly proportional.

Show question

Question

Can voltage dividers be used as signal attenuators?


Show answer

Answer

Yes, voltage dividers can be used as signal attenuators.

Show question

Question

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

Show answer

Answer

When the voltage value is too big.

Show question

Question

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?


Show answer

Answer

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

Show question

Question

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


Show answer

Answer

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

Show question

Question

What are logic level shifters used for?


Show answer

Answer

To connect two logic circuits.

Show question

Question

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


Show answer

Answer

The circuits will be damaged.

Show question

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?


Show answer

Answer

True.

Show question

Question

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


Show answer

Answer

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

Show question

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.

Show answer

Answer

5.13Ω

Show question

60%

of the users don't pass the Electric Current quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Just Signed up?

Yes
No, I'll do it now

Sign up to highlight and take notes. It’s 100% free.