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Exam Lessons

Electric current, Resistance, Electromotive Force (EMF), Circuit diagram

Electric Current

Definition of Electric Current

Electric current (l) is defined as the time rate of flow of electric charge along a conductor.

I=Qt

Q is the quantity of charge measured in Coulomb,  ‘t’ is the time in second . I is the current in Ampere(A).There are submultiples of Ampere

1mA = 10-3A

1μA = 10-6A

Ammeter is an instrument used for measuring current.

Milliameter measures smaller current.

Galvanometer are used to detect very small current.

Electric Circuit

https://www.slideshare.net/slideshow/embed_code/key/zw4X0BlXKRIEpnElectric Circuit Symbols Element Set for PowerPoint – SlideModel from SlideModel

Definition of Electric Circuit

An electric circuit is the path provided for the flow of electric current.

An electric circuit is a system that consists of the source of electricity, the key or switch and the connecting wires, ammeter to measure the current, voltmeter to measure the potential difference, Resistor or load and a rheostat to adjust the flow of current

electric circuit

Circuit Diagram

electric-circuit

Closed Circuit

It is a circuit in which there is no gap (key closed) along the conducting path.

closed circuit
open-short-circuit

Potential Difference (V)

The potential difference between any two points in an electric field is defined as the work done in moving a positive charge of 1 coulomb from one point in the electric field to another. Potential difference is measured in volts.

Voltmeter is used to measure potential difference.

V=WorkCharge

Electromotive Force

Electromotive force is defined as the total work done in driving one coulomb of electricity round a closed circuit or the total energy per coulomb obtained from a cell or battery.

E.m.f=WorkCharge

Electromotive force can also be defined as the potential difference across the terminal of a cell when it not delivering current to an external circuit or the potential difference across the terminal of a cell when it is in an open circuit.

Resistance

This can be defined as the opposition to the flow of charges (electrons) or current. Its S.I unit is Ohm. It is measured using Ohmmeter.

Types of Resistors

  1. Fixed/standard resistor:They have fixed resistance. The electrical symbol is fixed resistor
  2. Variable resistor: They are those resistors whose resistance can be varied such as Resistance box and Rheostat. The electrical symbols are variable resistor

EVALUATION

  1. Define the following terms (i) Resistor (ii) Electromotive force (iii) Current (iv) Lines of force (v) Potential difference

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