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Electric current is the flow of charge in an electric circuit. Electric current is measured by an ammeter. There are various measurement methods as well as units of current. The SI unit of current is Ampere or Amp. Ampere measures the flow of electric charge across a surface at a rate of one coulomb per second. The current in a circuit is used for generating heat, causing circuits to switch on, etc. Sometimes both the ions and electrons carry the charge at the same time.
| Table of Content |
Key Terms: Ampere, Ammeter, Unit of Current, SI Unit of Electric Current, Amps Electricity, Voltage, Power, Capacitance, Resistance, Inductance, Electric Field
What is Electric Current?
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The electric current is the flow of current or charge in electric circuits in terms of scientific understanding. The charge is sometimes simultaneously carried by the ions and electrons. The charge of the current needs to be measured by flowing through the circuit.
Electric Current
It determines the performance of the circuit and the circuit to operate as required. Electric current is measured by an ammeter and its unit is Ampere or Amp. However, nowadays there are different measurement methods for measuring the unit of current.
Discover about the Chapter video:
Current Electricity Detailed Video Explanation:
What is the SI Unit of Current?
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The SI unit of current is ampere by which the flow of electric charge across a surface at the rate of one coulomb per second is measured. As the charge is measured in coulombs and time in seconds, the unit is coulomb/Sec (C/s) or amp. He is largely credited as the father of Electromagnetics. And the formula for electric current is given as follows:
| I = V/R |
Where,
- I = Electric current
- V = Voltage
- R = Resistance of Material
Unit of Ampere
One ampere is roughly equivalent to approx 6.24×1018 elementary charges passing a given point in one second.
- Physicists believe the current to flow from a moderately positive point towards a somewhat negative point; this is called standard current.
- Like many other units, Ampere also has a symbol of its own – A.
- Many times Ampere is written as amp. Ampere is a vital unit in the international unit system because other units can be obtained from it.
Read More:
| Important Topic Related Links | ||
|---|---|---|
| Meter Bridge | Potentiometer | Cells In Series and Parallel |
| Electromotive Force | Carbon Resistor | Types of Current |
| Electrical Current | Circuit Diagram | Electrical Charges |
Standard Electric Units
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Although Ampere is a vital unit of measurement, to measure different properties we use different units. Electric properties like the voltage, power, capacitance, resistance, inductance, electric field, electric charge, frequency, the magnetic flux can be measured through their standard units.
| Parameter | Measuring Unit | Relationship |
|---|---|---|
| Voltage | volt (V or E) | |
| Current | amp (I) | |
| Resistance | ohm (R or Ω) | |
| Conductance | mho (G or ) | |
| Power | watt (W) | or |
| Inductance | henry (L or H) | |
| Capacitance | farad (C) | |
How to Measure Unit of Current?
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Electric current is measured through an ammeter, which measures the electric current in the ampere. Electric current on the load is measured with the help of ammeter by linking it in series to the load. Also, an ammeter has zero resistance.
The reason for not linking the ammeter in parallel to the load is that the ammeter has minimal resistance. If it is linked in parallel, it will become a short circuit path and will allow current to pass through it, hence burning down the wire.
What is meant by Ampere?Ampere can be expressed as the unit of electric current which is equivalent to the flow of one Coulomb per second. How can be Ampere measured?Ampere meter, also known as an Ammeter is an electrical instrument used to measure electrical current in Amperes. Is it possible that Ampere can be negative?Yes, the value of ampere can also be negative. Why do you think is Ampere required?Ampere is primarily required in order to quantify the current flowing in a system. |
Read More: Difference Between Ammeter and Voltmeter
Types of Ammeter
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Types of ammeter are based on the structure of the ammeter and the type of current that flows through it. Based on the structure of the ammeter, ammeters are categorized as follows:
- Moving arm ammeter
- Rectifier Type Ammeter
- Permanent moving coil ammeter
- Electro-dynamometer ammeter
Based on the type of current that flows through them, the ammeter is categorized as follows:
- DC ammeter
- AC ammeter
Electrical Units and Symbols
Here are some of the electrical units and their respective symbols:
| Electrical Value | Measuring Unit | Unit Symbol |
|---|---|---|
| Voltage | Volt | V or E |
| Capacitance | Farad | C |
| Resistance | Ohm | R or Ω |
| Charge | Coulomb | Q |
| Inductance | Henry | L or H |
| Impedance | Ohm | Z |
| Power | Watts | W |
| Frequency | Hertz | Hz |
| Conductance | Siemen | G or ℧ |
Things to Remember
- The SI unit for electric current is Ampere or amp.
- The value of 1 Ampere is equal to the flow of charge of 1 coulomb in 1 second. The amount of current is associated with the amount of charge flowing per second.
- The device used for measuring an electric current is an ammeter.
- The ampere is an internationally recognized and accepted unit of current since 1908 and has been measured progressively better with the progress of measuring instruments.
- The electric current is the flow of current or charge in electric circuits in terms of scientific understanding.
- One ampere is roughly equivalent to approx 6.24×1018 elementary charges passing a given point in one second.
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Previous Year Questions
- If now we have to change the null point at 9th wire, what should we do?… [ DUET 2007 ]
- The electrical permittivity and magnetic permeability of free space are… [ DUET 2003 ]
- Just after key K is pressed to complete the circuit, the reading will be …. [ KEAM 1999 ]
- The resistance between any two terminals is when connected in a triangle is…. [ NEET 1993 ]
- potential drop through 4Ω resistor is… [ NEET 1993 ]
- The potential difference per unit length of the wire will be… [ NEET 1999 ]
- Value of R for which the power delivered in it is maximum is given by... [ NEET 1992 ]
- In the circuit shown, current (in A) through the 50 V and 30 V batteries are, respectively…..[JEE Main 2014]
- In the electric network shown, when no current flows through the 4Ω resistor…
- In the above circuit the current in each resistance is….
- Find the internal resistance of the cell... [JEE Mains 2018]
- In vertical circular motion, the ratio of kinetic energy of a particle…. [MHT CET 2016]
- The motion of a particle in straight line is…. [JKCET 2013]
- A charged particle enters a uniform magnetic field with a certain speed …. [JKCET 2006]
- From the top of a tower a body AA is projected vertically up…. [JKCET 2007]
Sample Questions
Ques. What is the SI for electric current? (1 mark)
Ans. Ampere or amp is the SI unit for electric current. It is denoted by the letter A.
Ques. What is the value of C used while deriving the ampere? (1 mark)
Ans. When deriving Ampere, the value of C was taken as 6.24×1018 charges.
Ques. What is Electric Current? (1 mark)
Ans. Electric current can be defined as the rate of the flow of electrons in a conductor.
Ques. How is Electric Current measured? (2 marks)
Ans. Electric Current can be measured in coulombs per second. The SI unit of current is Ampere or amp. One Coulomb of charge moving past a point in one second equals one ampere. When 6.241 x 1018 electrons flow through an electric frame in one second, it consists of one Ampere.
Ques. When electrons drift in a metal from lower to higher potential, does it signify that all the free electrons of the metal are moving in the same direction? (Delhi 2012)
Ans.
No, only the drift velocities of the electrons are superposed over their random or haphazard thermal velocities. The solid line shows the random path followed by a free electron in the absence of an external field. The electron proceeds from A to B, making six collisions on its path. The dotted curve shows how the random motion of the same electron gets modified when an electric field is applied.
Ques. Show the variation of resistivity with temperature for a typical semiconductor on a graph. (Delhi 2012)
Ans.
Here, the resistivity of a semi conductor decreases rapidly with temperature.
Ques. A 10 v battery with a negligible internal resistance is connected across a 200 V battery and a resistance of 38Ω as shown in the figure. Find the value of the current in circuit. (Delhi 2013)
Ans. Applying Kirchhof s rule, we get 200 -10 = 190 V
and I = V/R = 190/38 = 5A
Ques. In the circuit diagram the network PQRS, has the batteries of 4 V and 5 V and negligible internal resistance. A milliammeter of 20 Ω resistance is connected between P and R. Calculate the reading in the milliammeter. (Comptt. All India 2012)
Ans. Applying loop rule to loop PQRP
-4 = 60(I – I1) – 20 I1 = 0
or – 4 = 60I – 60I1 – 20I1
or 20I1 -15 I = 1 …[+ by 4 …(i)]
Applying loop Yule to loop PRSP, we get
-5 + 200 I + 20 I1 = 0
4I1 + 40 I = 1 …[+ by 5 …(ii)]
Therefore, Reading of milliammeter = 0.064 A.
Ques. Define the term ‘Mobility’ of charge carriers in a conductor. Write its S.I. unit. (Delhi 2014)
Ans. Mobility of charge carriers can be defined as the magnitude of the drift velocity per unit electric field E.
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