E.M.F = Terminal voltage + Voltage drop inside the source of supply.
The E.M.F can not be measured because the measuring instrument will cause some voltage drop due to consumption of some energy and the actual value will not come in appearance.
Voltage law :- The algebraic sum of the electromotive forces in any closed circuit or mesh is equal to the algebraic sum of the products of the resistance of each portion of the circuit and the currents flowing through them.
Kirchhoff’s laws are applicable to both a.c and d.c circuit. In case of a.c circuit any e.m.f of self inductance or that existing across a capacitor should be taken into account.
In mechanic power is simply the rate of doing work. Electrical power is the rate of transfer of electrical energy i.e the rate of electrical work done to mark a flow of change ‘Q’ under a potential difference ‘V’.
In mechanics energy is simply the capacity of doing work. Electrical energy is the amount of work done which is equal to the product of the rate of doing work by time i.e power x time.
Metric horse power is said to be the mechanical unit of power in M.K.S. system when it does the work at the rate of 75 kg-m/sec or 4500 kg-m/minute.
H.P (Metric) = 735.5 watts = o.7355 kW.
W = V.I,
W = I^{2}R.
In unit relation, Watt = ((Volts)^{2})/(Ohm.)
Therefore, the resistance of lower wattage 25 W lamp will be more than higher wattage 200 W. lamp.
The resistance will be halved for half length.
Therefore W_{2} = V^{2}/(R/2) = 2. V^{2}/R = 2× W_{1}
If W_{1} =1000 W. then for half length, W_{2} = 2 × 1000W = 2000W.
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