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