1 volt = 1 joule/1 coulomb
or
1 V = 1J/1C
14. Galvanometer:
It is device to detect current in an electric circuit.
15. Ammeter:
It is device to measure current in a circuit. It is always connected in series
in a circuit.
16. Voltmeter:
It is a device to measure potential difference. It is always connected in
parallel to the component across which the potential difference is to be measured.
17. Ohm’s law:
This law states that the current passing through a conductor is directly
proportional to the potential difference cross its ends, provided the physical conditions
like temperature, density etc. remains unchanged.
V α I
or
V = RI
The proportionality constant R is called resistance of conductor.
18. Resistance:
It is a property of a conductor by virtue
of which it opposes the flow of
current through it. It is equal to the ratio of the potential difference applied across its
ends and the current flowing through it.
Resistance = Potential difference/Current
or
R = V/I
19. Ohm:
It is the S.I. unit of resistance. A conductor has a resistance of one ohm if a
current of one ampere flows through it on applying a potential difference of one volt
across its ends.
1 ohm = 1 volt/1 ampere
or
1Ω = 1V/1A
20. Factors on which resistance of a conductor depends:
The resistance R of a
conductor depends
i) Directly on its length L i.e. R α L.
ii) inversely on its area of cross-section A i.e. R α 1/A
iii) on the nature of material of the conductor on. On combining the above factors, we get R α L/A R = ρ * L/A The proportionality constant ρ is called resistivity of conductor.
21. Resistivity:
It is defined as the resistance offered by a cube of a material of side 1 m
when current flows perpendicular to its opposite faces. Its S.I. unit is ohm-meter
(Ωm).
Resistivity, ρ = RA/L
22. Equivalent resistance:
If a single resistance can replace the combination of
resistances in such a manner that the current in the circuit remains unchanged, then
that single resistance is called the equivalent resistance.
23. Laws of resistances in series:
i) Current through each resistance is same.
32

ii) Total voltage across the combination = Sum of the voltage drops.
V= V
1
+ V
2
+ V
3
iii) Voltage drops across any resistor is proportional to its resistance.
V
1
= IR
1
, V
2
= IR
2
, V
3
= IR
3
iv) Equivalent resistance = Sum of the individual resistances.
R
s
= R
1
+ R
2
+ R
3
v) Equivalent resistance is larger than the largest individual resistance.
24. Laws of resistances in parallel:
i) Voltage across each resistance is same and is equal to the applied voltage.
ii) Total current = Sum of the currents through the individual resistances.
I = I
1
+ I
2
+ I
3
iii) Currents through various resistances are inversely proportional to the individual
resistances.
I
1
= V/R
1
, I
2
= V/R
2
, I
3
=
V/R
3
iv) Reciprocal of equivalent resistance = Sum of reciprocals of individual resistances.

#### You've reached the end of your free preview.

Want to read all 163 pages?

- Fall '14
- Chemical reaction, N.C.E.R.T Text book