Class 12th is a milestone for all of us, the exam tensions, the chase to get a high percentage, the search for a perfect course and university are some common issues that we all face. Out of all the 3 class 12th streams, Science is regarded as the toughest one. Ranging from long theorems to difficult calculations, the stream keeps the students occupied the whole academic year. Physics, in particular, holds special importance for those who want to make a career in Engineering and Technology. Current Electricity is an important Class 12th Physics chapter that is asked in various engineering entrance exams and SAT Subject test. Through this blog, we aim to provide some essential notes for Current Electricity.
Class 12 Physics chapter Current Electricity comprises of various other subparts. In this blog, we are going to explain Electric Charges & Fields, Electrical Conductivity, Electrostatic Potential, Capacitance & Moving Charges, and Magnetism. Given below is the list of all the topics that are a part of current electricity physics syllabus class 12:
- Electric Current
- Electric Currents in Conductors
- Ohm’s Law
- Drift of Electrons and the Origin of Resistivity
- Limitations of Ohm’s Law
- Resistivity of various Materials
- Temperature Dependence of Resistivity
- Electrical Energy, Power
- Combination of Resistors: Series and Parallel
- Cells, emf, Internal Resistance
- Cells in Series and in Parallel
- Kirchhoff’s Laws
- Wheatstone Bridge
- Meter Bridge
Electric Charges and Fields: Electrical Conductivity
Charge can be defined as the flow of current which is directly proportional to the resistance offered by a resistance R. Electric conductivity is an inverse of resistance for a conductor of electricity but the specific resistance is the resistance of the material per unit cube. The relation is defined as:
Where constant and is resistivity
Here are some important notes on the topic Conductivity of Current Electricity:
- The rate at which the flow of charge takes place through any cross-section of a conductor is called electric current flowing through it.
- Mohm is the measurement to estimate total resistance in a conductor
- The current density vector provides current per unit area flowing through area when it is held normal to the direction of charge flow. Note that the direction of is in the region of the current flow.
- In solid channels like metals, the valence electrons of the atoms do not remain attached to individual atoms but are free to move throughout the volume of the conductor.
- Under the effect of an external electric field, the valence electrons move in a definite direction causing electric current in the conductors. Thus, valence electrons are the current carriers in solid conductors.
- Current is also carried by liquids: In electrolysis like CuSo, NaCi etc., there are positively and negatively charged ions (like Cu”. So,Na’.CT).
- These are forced to move in definite directions under the effect of an external electric field, causing electric current.
Kirchoff’s law states the total sum of changes in the potential difference in any closed loop connected with the N number of resistors must sum to zero. This is based on the principle that electrostatic forces alone cannot do any work in a closed-loop since this work is equal to the potential difference, which is zero if we start at one point of the loop and come back to it.
This gives: (R1 + R2) I1 + R3 Iv3 + R4 I4 = 0
- Thus, in solutions, the current carriers are positively and negatively charged ions. Current carriers in gases: Ordinarily, the gases are insulators of electricity.
- Mobility is determined to be the measurement of drift speed per unit electrical field.
from this formula charge Q is the electric charge of the current carrier and is its mass.
- If the current flows through a conductor then the Resistivity is assigned to be reciprocal of the current conductivity
the difference between mass and current comes to be ()
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Electrostatic Potential and Capacitance
Wheatstone bridge is a simple circuit for measuring an unknown resistance by connecting it so as to form a quadrilateral with three known resistances and applying a voltage between a pair of opposite corners.its made by arranging four resistances which are R1, R2, R3, R4.
The circuit can be in balanced condition if the amount of charge is equal in all resistors R . Apart from that R1, R2, R3 are known,and using this bridge R4 can be determined
Electronic Devices Emf of the Cell (E)
An electric cell works on the principle of the flow of current in the circuit. An electromagnetic field (EMF) can be defined as the potential difference across the terminals of a cell when it is not supplying any current and EMF is generated in the circuit due to the following factors:
The potential difference (V): The voltage across the terminals of a cell when it is supplying current to external resistance is called potential difference or terminal voltage. Potential difference is equal to the product of current and resistance of that given part ie. V=R.
Internal resistance (R): internal resistance is the total resistance of a cell in a circuit.and in an electric cell its created by the opposition of electrolyte to the flow of current however the internal resistance of a cell is proportional to the distance between two electrodes (r d) and the area of electrodes. If a cell has zero internal resistance then the cell is said to be in ideal state.
Specific resistance: The electrical resistivity of the material of a conductor is defined as the resistance of a unit length with unit areas of the cross-section of the material of the conductor.
Unit and dimension: It’s S.I. unit is ohm and dimension is [ML’T’A] Resistivity is the intrinsic property of the substance. It is independent of the shape and size of the body
Moving Charges and Magnetism
A charge can generate a magnetic field if it is in action. The magnetic field can also combine with a moving charge called Lorentz Force which depends on q, v, and B. The potentiometer is a device to compare the potential differences across two or more points referred to as (N) Because the arrangement of the circuit involves no current flow if the key K2 is disconnected the device can be used to measure potential differences and EMFs of two sources.
Resistivity is given as,
Where, is the resistivity of the material and is the temperature coefficient of resistivity
- The total sum resistance R of n resistors when joined in a parallel circuit
, where is a constant of proportionality called electrical conductivity. This statement is one possible form of Ohm’s law.
- Total resistance R of n resistors connected in series is given by R = R1 + R2 + … + Rn
These were some of the important points on Current Electricity that will definitely help you in getting a high score. Choosing the right career path after class 12th can take you to great heights. To make a well-informed decision, let Leverage Edu help you out. Book an e-meeting with our experts and be sure of which career you want to pick!