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Think of your phone charger- that moment when you switch it on, and there is an electric flow to charge your phone, that is a real-life example of the concepts in Class 12 Physics Chapter 3: Current Electricity. We explore the underlying concepts of electric currents, resistances, circuits, and flow of charge in conductive materials a very important concept in the way electronic devices operate in this chapter of NCERT Notes.
This chapter is an essential part of the CBSE Class 12 Physics curriculum, and at the same time, essential to JEE, NEET, and other competitive exam candidates because it reinforces the conceptual understanding of concepts such as Ohm Law, Kirchoff Law, internal resistance of cells, Wheatstone bridge, meter bridge, and resistivity and conductivity. Being good at these concepts will lay a foundation in solving theoretical and numerical problems in exams. In order to facilitate students in revising the topics well, Careers360 provides well-organised NCERT Notes of Class 12 Chapter 3 Current Electricity, developed through the efforts of experienced Physics teachers. This revision notes include summaries of the main concepts with fast learning, an extended list of significant formulas, neatly labelled diagrams to support visual understanding, solved sample questions to improve problem-solving ability
Also, students can refer,
Download the PDF version of Current Electricity NCERT Notes to view them offline. Using these notes, students can revise anytime without the internet and is most suitable for fast and easy access.
The NCERT Class 12 Physics Chapter 3 Notes – Current Electricity provide a clear and concise summary of essential concepts like Ohm’s Law, Kirchhoff’s Laws, and circuit analysis. These notes are ideal for quick revision and exam preparation for CBSE, JEE, and NEET.
Where, i is the current, q is the charge and t is the time.
Where, σ is conductivity and ρ is resistivity or specific resistance of the substance
Where, μ is mobility and vd is drift velocity
R- Electric Resistance
where ρ is resistivity / specific resistance, l is the length of the conductor and A is the area of the cross-section of the conductor
,
Where, m is the mass, n is the number of electrons per unit volume, e is the charge of the electron, and τ is the relaxation time.
ρ=ρo(1+α(T−To))
ρ: Resistivity at temperature T
ρo: Resistivity at temperature To
Temperature Coefficient of Resistance
Where the value of
The carbon resistance typically consists of four coloured ring bands labelled as A, B, C, and D.
Tolerance of Gold is ±5%
Tolerance of Silver is ±10%
Tolerance if no colour ±20%
Series Grouping of resistance
For nidentical resistance:
Parallel Grouping of Resistance:
If two resistances are in Parallel:
r∝d
r∝A
r∝c
r∝1/temp
Cell supplies a constant current in the circuit.
Where, R- External resistance and r- internal resistance
In series grouping anode of one cell is connected to the cathode of other cells
- Equivalent e.m.f of combination is
- Equivalent internal resistance
- Main current / current from each cell
- Power dissipated in the external circuit is
- Conditions for Maximum Power is
-
In parallel grouping, all anodes are connected to one point and all cathode together at other points
For n cells connected in parallel
Equivalent e.m.f
Equivalent internal resistance
The main current is
The potential difference across the external resistance
Current from each cell
The power dissipated in the circuit
Condition for Maximum Power
∑i=0
i1+i3=i2+i4
This law is simply based on the conservation of charge.
∑V=0
In closed-loop
It is an arrangement of four resistances that can be used to measure one of them in terms of rest
(Balanced condition)
No current will flow through the galvanometer
unbalanced condition:
Current will flow from
Q1: n identical cells, each of e.m.f. E and internal resistance r, are connected in series. Later on it was found out that two cells ' X ' and ' Y ' are connected in reverse polarities. Calculate the potential difference across the cell ' X '.
Answer:
Two cells are connected in reverse polarity
So total emf
potential difference across cell
Q2: Two batteries of emf's 3 V and 6 V and internal resistances 0.2Ω and 0.4Ω are connected in parallel. This combination is connected to a 4Ω resistor. Find the equivalent internal resistance of the combination
Answer:
Given:
Two batteries are connected in parallel, and then connected to an external resistor of
Battery
Battery
The equivalent internal resistance of the combination is calculated using the formula:
Substitute the values into the formula:
Hence, the equivalent internal resistance of the combination is 0.133 ohm.
Q3: Two wires P and Q are made of the same material. The wire Q has twice the diameter and half the length as that of wire P. If the resistance of wire P is R, the resistance of the wire Q will be:
Answer:
NCERT Class 12 Physics Chapter 3 Notes |
Current Electricity carries significant weight in the Physics board exam, accounting for around 10% of the total marks. It covers fundamental concepts that form the base for other chapters and practicals.
Yes, this chapter is very important for entrance exams such as JEE Main and NEET. Questions based on Ohm’s Law, circuits, and resistivity often appear in these exams.
Start with simple problems and gradually move to complex circuits. Practice daily, understand formulas, and use Kirchhoff’s and Ohm’s Laws effectively to solve questions step-by-step.
A Wheatstone Bridge is a network of four resistors used to precisely measure unknown resistance. It is widely used in sensor applications like strain gauges and temperature measurement.
In most conductors, resistance increases with an increase in temperature due to more frequent collisions between electrons and atoms. However, in semiconductors, resistance decreases with temperature.
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