electric circuit , resistors in parallel definition and diagram

Electric circuit, difference types

What is electric circuit? It is part through which electric current flows. Electric circuit must consist of the cells or battery, load or resistor, and switch or key.  There are three types of electric circuits; Open, closed and short circuit.  

Open circuit: A circuit is said to be open when there is gap between the sources and loads, so that there will be no flow of current

Electric circuit

Short circuit: A circuit is said to be short circuited when, the terminals of source are connected together without any load (bulb) connected to the circuit.

Electric circuit

Closed circuit: A electric circuit is said to be closed when there is no gap between the source and circuit component like bulb, so that the current will flow from the source and light up the lamp or bulb.

Electric circuit

Arrangement of cells and resistor in electric circuit

Cells and resistors can be connected in circuits either in series of parallel. Though many electric networks may require the combination of series and parallel connections Electric Circuit showing the arrangement or cells and resistors

Electric  circuit

The above circuit shows the connection of cells in series with a series and parallel combinations of resistance.

 Electric circuit of Wheatstone bridge

Electric circuit

The electric circuit above was designed by Wheatstone, around 1843. It is a bridge circuit which is used to measure the resistance accurately. It consists of four resistors of resistance R1, R2, R3, and R4, connected as shown above.

Electric circuit that we can use to verify Ohm’s law.

What is Ohm’s law? It states that a current passing through a metallic conductor is directly proportional to the potential difference p.d, across the two terminals provided the temperature is kept constant. That V=IR.

So the circuit below can be used to verify the law.

Electric circuit

The electric circuit above consists of battery B, a key K, a resistor R, rheostat Rh, an ammeter A, and a voltmeter V.

To verify ohm’s law, we start by setting of Rh to a large value, the key k is closed and the reading of V and A are taken. The setting of rheostat Rh, is gradually reduced to obtain series of readings of potential difference v, and current I. The procedure is repeated four more times, and then the reading is tabulated as V (volts) and I (ampere). The graph of v against I is plotted and the straight line passing through the origin is obtained. So the slope ∆V/∆I gives the value of resistance R in ohms.

Electric circuit of potentiometer

What is potentiometer? It is electric device use in measuring and comparing e.m.f of cells.

Electric circuit



In the electric circuit in the diagram above, can be described as a circuit for potentiometer. Here a cell E1 is connected as shown through a galvanometer (represented by arrow) and a balanced point is obtained at D1, this means that e.mf E1 =kL for E1. When a second cell E2 replaces E1, a new balance is obtained at D2, that is E.m.f E2  = kL

Now the e.m.f of the both cells E1 and E2 can be compared. If one of them a known, the e. mf of the other can be calculated using

E1/E2 =L1/l2

Example: A potentiometer wire carrying a steady current is 100cm long. When a standard cell of e.m.f 1.5v is connected to a balance length of 60.0cm was obtained. Calculate the e.m.f of a cell that gives a balance length of 80.0cm.

Solution, using E1/E2= L1/L2, Where E1= 1.5v, L1= 60cm, and L2= 80.0cm

Therefore 1.5/E2 =60/80

E2 = 4 x 1.5/ 3= 2.0v

E2=2.0v

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