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Electrical Current is the rate of movement of electrons (negatively charged) in conductors. The SI Unit of electric current is Ampere, denoted by the letter ‘A’. One ampere is the current passing through a substance where there is a flow of one coulomb of charge in one second. Electrical current is denoted by the letter ‘I’. The electrical charge carriers of current can be electrons, protons (positively charged) or ions (atoms which have lost one or more electrons)
Read More: Current Electricity
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Key Terms: Ohm’s law, Electrical Current, Drift Velocity, Alternating Current, Direct Current, Electric Charge, Ampere, Electric Charge, Electrons
What is Electrical Current?
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The free movement of electrons is electrical current. The quantity of electrons that moves determines the ability of a material to conduct electricity. Materials are classified as conductors and insulators based on the power to conduct electricity.
Electrical Current
- Conductors are substances that allow the electrons to move freely and that movement of electrons helps in conducting electricity. Examples: iron, silver, and salt solution.
- Insulators are materials that prevent the transfer of electrons thus not allowing the electrons to conduct electricity. Example: plastic, rubber and wood.
The video below explains this:
Electrical Current Detailed Video Explanation:
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Properties of Electric Current
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Some of the interesting properties of electrical current are as follows:
- Flow of electrons generates electrical current.
- Work done to move the electron stream from one conductor to another is called as Electrical energy.
- Electrical energy can be converted to other energy forms like light or mechanical energy.
- Electrical current can be classified as – AC and DC.
- DC is used a primary energy source in industries and low voltage applications.
- AC is used prediominantly in household and commercial spaces.
- Electrical current is measured in Amperes using an ammeter.
- The conventional direction of electrical current is from positive terminal to the negative terminal of the battery.
Conventional Flow Vs Electron Flow
- Positive charge flow is the conventinal direction of current flow.
- Electrons being negatively charged are attracted to the positive charges.
- Electron thus always flow from the negative to the positive terminal.
Also Read: Resistance and Length Relation
Types of Electrical Current
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There are two types of electrical current:
- Direct Current (DC)
- Alternating Current (AC).
AC and DC Current
Direct current (DC)
In Direct Current, the direction of current will not be changed and will move in a single direction, mostly all types of batteries use direct current only. Examples- computer, telephones, satellites.
Alternating current (AC)
The movement of electric charge reverses direction in a periodic pattern in its system. Alternating Current is a category of electric power that is delivered to businesses and residences. Audio and radio signals carried on electrical wires are some examples of AC.
Also Read: Phasor Representation AC
Effects of Electric Current
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There are three effects of electrical current:
- Magnetic Effects
- Chemical Effects
- Heating Effects
Magnetic Effect
Electrical current shows a magnetic effect which is commonly known as electromagnetic effect. We have studied that whenever a magnet passes through an electric current conductor, it creates a magnetic field.
Field Lines of Magnet
Chemical Effect
Whenever we take a conductor solution and pass an electric current through it, then
- Bubbles will be produced
- Metal deposits will be seen on the electrodes
- May lead to change in colour of chemical solution.
This depicts the chemical effect of electrical current. The solution gets ionized and breaks down into ions. This is usually seen in the case of batteries.
Chemcial Effect of Electric Current in a Battery
Heating Effect
When an electrical current is allowed to pass through the conductor object, then it will produce heat. This depicts thee hating effect of electrical current. Heating effect is given by the following equation which describes the relation between the heat produced and electrical current through a conductor.
H= I2RT
Where,
H- Heat produced in Joules
I – Electrical current in Amperes
R – Electrical Resistance in Ohms
T - Time in Seconds
Ohm's Law
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Ohm's law is one of the most important laws in the field of electrical current. It helps in determining the relationship between electrical current and potential difference. This law was named after a German Physicist, George Simon Ohm. The law is applicable for current flowing through conductors and states that,
The electric current flowing through a conductor is directly proportional to the amount of voltage applied on it.
Ohm's Law
Mathematically the law can be represented as
V = I R
V denotes voltage across the conductors
I indicate the electrical current which is flowing through the conductors
R denotes the amount of resistance.
Ohm's law plays an important role in calculating the amount of electric power and the relation is given by, P =VI
Applications of Ohm’s Law
- Helpful in determining the level of voltage and resistance.
- Plays a crucial role in maintaining the desired voltage across the various electronic components.
- Used in diverting electrical current through usage of DC ammeter.
Drawbacks of Ohm's Law
- Does not work for electrical elements which allows flow of current in a single direction only. Example- transistors.
- Works only in the condition where the temperature is provided and other physical factors remain constant. The best example of it is filament of a bulb
Read Also: Ohm’s Law And its Limitations
Drift Velocity
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Electrons have a tendency of moving around all the time, but when they come into an electric field, they moves toward a particular direction (where the electric field is applied).The average velocity at which these electron drifts is called drift velocity,or can be called the average velocity of an electron.
Drift Velocity
Drift Velocity Formula
The formula used to calculate drift velocity is
I = nAvQ
where I is electrical current
n is the number of electrons
A is area of conductor
v is the drift velocity
Q is the charge of an electron
The standard unit of drift velocity is m/s.
Read Also: NCERT Solutions Chapter 3 Current Electricity
Resistive Heating and Electrical Current
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Resistive Heating is also known as resistance, ohmic or joule heating . It is a simple process in which a heat is produced when electric current passes through a conductor. This happens due to friction. The process is now very commonly used in home appliances like toasters and electric heaters.
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Measurement of Electrical Current
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Current can be measured using an ammeter. It is also measured by detecting the magnetic field associated with the current.
Techniques to Measure Current
- Shunt resistors
- Hall effect current sensor transducers
- Transformers
- Magnetoresistive field sensors
- Rogowski coils
- Current clamps
Discover about the Chapter video:
Current Electricity Detailed Video Explanation:
Things to Remember
- Electrical current is movement of free electrons in a conducting material.
- The unit of electrical current is Ampere.
- Ohm’s law is applicable to conductors wherein the potential difference across the conductor is directly proportional to the current flowing through it.
- Electrical current is of two types- alternating and direct.
- Flow of electrons is from negative to positive whereas the conventional current flow direction is from positive to negative terminals.
- Electrical current is governed by magnetic, chemical and heating effects.
- Drift velocity is the electron tendency to move in a particular direction in the presence of an electric field.
- Resistive heating is produced in a conductor when electrical current passes through it.
Also Check : Class 12 NCERT Text Books
Previous Year Questions
- When the switch S , in the circuit shown, is closed, then the value of current ii will be…. [ JEE Main 2019]
- The Wheatstone bridge shown in Fig. here, gets balanced when the carbon resistor… [JEE Main 2019]
- In the given circuit the cells have zero internal resistance…. [JEE Main 2019]
- The currents I2,I3 and I6,respectively, are….[JEE Main 2019]
- In the given circuit, an ideal voltmeter connected across the 10Ω resistance reads 2V . The internal resistance rr, of each cell is….[JEE Main 2019]
- In the experimental set up of metre bridge shown in the figure, the null point is obtained at a distance…. [JEE Main 2019]
- Correct set up to verify Ohm’s law is….[JEE Main 2013]
- A d.c. main supply of e.m.f. 220V is connected across a storage battery of e.m.f. 200V through a resistance of 11 Ω…... [JEE Main 2014]
- The percentage change in its electrical resistance if its volume remains unchanged is…. [JEE Main 2019]
- three resistors 3Ω,9Ω and 9Ω and a capacitor….. [JEE Main 2013]
- If now we hav.e to change the null point at 9th wire, what should we do?…
- The electrical permittivity and magnetic permeability of free space are…
- 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 ]
Sample Questions
Ques. State Ohm's law. (1 Mark)
Ans. Ohm's law is used in the field of electric current to find out the relation between the electric current and potential difference. The law states that the voltage produced across a conductor will be directly proportional to the electric current.
Ques. Define the term 'drift velocity'. (1 Mark)
Ans. Drift velocity is the term which is the average of velocity gained by the charged particles i.e. electrons due to the electric field .
Ques. What do you mean by conventional flow of current? (1 Mark)
Ans. As we know that electrons flow from negative end to positive end, but conventional flow of current flows from positive to negative end we can simply call it as the conventional flow of current.
Ques. Conventional current moves from which direction? (1 Mark)
Ans. Conventional current of flow moves from positive terminal to negative terminal , which is just the opposite of normal electrons.
Ques. What is the relation between current and voltage? (1 Mark)
Ans. Ohm's law is used to find the relationship between the current and voltage. According to this law
Ques. Mention the case where Ohm's law is not applicable. (1 Mark)
Ans. Ohm's law will not work in cases where temperature and other factors remain unchanged and if the current flows in a single direction only , then it will fail the law.
Ques. How much current is produced by a voltage of 18 kV across a 15 k resistance? (1 Mark)
Ans. I=V/R
=18/15
= 1.2 ampere of current
Ques. What is the voltage source for a circuit carrying 2 A of current through a 36 resistor? (1 Mark)
Ans. I =2AR
36ohmV = 2*36V = 72V
Voltage = 72V
Ques. Explain the effects of an electric current. (2 Marks)
Ans. The main effects of an electric current are :-
- Heating effect:- when the flow of current is passed through the conductor, then the heat will be produced.
- Magnetic effect:- As we have studied in previous classes, that a conductor carrying current develops a magnetic field .
- Chemical effect:- Whenever a current passes through copper solution, then the electricity will be produced and the effect will be known as the chemical effect of a chemical effect.
Ques. (a) Deduce the relation between current I flowing through a conductor and drift velocity of the electrons.
(b) Figure shows a plot of current ‘I’ flowing through the cross-section 5 of a wire versus the time ‘t’. Use the plot to find the charge flowing in 10s through the wire. (5 Marks) [Comptt. All India 2012]
Ans. (a) Relation between electric current and drift velocity : Consider a uniform metallic wire XY of length l and cross-sectional area A. A potential difference V is applied across the ends X and Y of the wire. This causes an electric field at each point of the wire of strength:
Due to this electric field, the electrons gain a drift velocity Vd opposite to the direction of the electric field.
The distance transversed by each electron in time (t) = drift velocity × time = Vdt
If we consider two planes P and Q at a distance Vdt in a conductor, then the total charge flowing in time t will be equal to the total charge on the electrons present within the cylinder PQ.
The volume of this cylinder = cross sectional area × length = A Vdt
If n is the number of free electrons in the wire per unit volume, then the number of free electrons in the cylinder = n(A Vdt)
If charge on each electron is -e (e = 1.6 × 10-19 C), then the total charge flowing through a cross-section of the wire,
This is the relation between electric current and drift velocity. Negative sign shows that the direction of current is opposite to the drift velocity.
(b) Charge = Current × time
(i) For 0 to 5 seconds, the current
Hence, q1 = (2.5) × (5) = 12.5 C
(ii) For 5 sec to 10 sec, the current = 5A
Hence, q2 = 5 × (10 – 5) = 5 × 5 = 25 C
q = q1 + q2 = 12.5 + 25 = 37.5 C
Ques. What is an Electromotive Force?
Ans. The motion of free electrons is normally haphazard. If a force acts on electrons to make them move in a particular direction, then up to some extent random motion of the electrons will be eliminated. An overall movement in one direction is achieved. The force that acts on the electrons to make them move in a certain direction is known as electromotive force and its quantity is known as voltage and is measured in volts.
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