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Emf (electromotive force) is the name given to a non-electrostatic agency. Typically, it is a battery in which a chemical process achieves this task of doing work in driving the positive charge from a low potential to a high potential.
The effect of such a source is measured in terms of work done per unit charge in moving a charge once around the circuit. This is denoted by ε.
Ohm’s law is obeyed by many substances, but it is not a fundamental law of nature. It fails if
When applied to a loop as shown above (which could be part of a larger circuit), this gives
-(R1 + R2) I1 - R3 I3 - R4 I4 = 0.
Points to remember in the case of current loops:
Choose any closed loop in the network and designate a direction (in this example, counter clockwise) to traverse the loop.
Go around the loop in the designated direction, adding emfs and potential differences. An emf is counted as positive when it is traversed from (−) to (+) and negative in the opposite case, i.e. from (+) to (−).
An IR term is counted negative if the resistor is traversed in the same direction of the assumed current and positive if in the opposite direction.
Equate the total sum to zero.
The Wheatstone bridge is an arrangement of four resistances—R1, R2, R3 and R4. The null point condition is given by
This is also known as the balance condition. If, for instance, R1, R2 and R3 are known, then R4 can be determined.
In a balanced condition of the meter bridge,
σ: Resistance per unit length of wire
ℓ1: Length of wire from one end where the null point is obtained
A potentiometer is a device to compare potential differences. Because the method involves a condition of no current flow, the device can be used to measure potential differences and the internal resistance of a cell and to compare the emfs of two sources.
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Please explain Ans is 8 ohm
A electric heater rated 220v and 550v is connected to ac mains the current drawn is?