Current Electricity Class 12 Notes Physics Chapter 3

Chapter at a Glance

1. According to ohm’s law, V oc I or V = IR
where Vis the potential difference in volt, I is the current in ampere, R is the resistance in ohm.

2. One way of writing Ohm’s law is J = crE, where j is current density, cr conductivity
and E electric field.

3. Ohm’s law cannot be applied to circuits which contain diodes, transistors, capacitors etc.
Ohm’s law and Kirchhoff’s loop theorem can be applied to AC voltages only for their instantaneous values. They cannot be applied to rms values.

7. When a uniform wire conductance ‘c’ is stretched ton times the original length, its conductance becomes c/n2.

8. Two important properties of a metal to make a standard resistor are low temperature coefficient and low linear expansivity.

9. Resistance is a property of object, resistivity is a property of material.

11. The cells are connected in series to get more voltage, in parallel to get more current and in mixed group to get more power.

16. The meter bridge cannot be used to measure very high or very low resistances.

17. In a potentiometer, if the EMF of the driving cell (cell connected in the main circuit) is increased, the balancing length will decrease.

18.When current I flows through a conductor of resistance R for time t, then heat generated in it is given by according to joule’s heating law.

19. A fuse wire should have low melting point and high resistivity.

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