# NCERT Class X Science Class: Chapter –12. Electricity – Part-5

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Question 19:

A child has drawn the electric circuit to study Ohm’s law as shown in Figure. His teacher told that the circuit diagram needs correction. Study the circuit diagram and redraw it after making all corrections.

The circuit diagram is not correct because of the following reasons:(i) Ammeter is connected in parallel with R and voltmeter connected in series with it in contrary of the fact that ammeter should be connected in series and voltmeter in parallel. This is so because same current flows in series and same voltage exist in parallel combination.(ii) The current is drawn from negative terminal and enter into the battery at possible terminal which is not possible in one battery circuit.(iii) Cells are not connected in series combination in the battery of the circuit. The correct diagram is given as follow:

Question 20:

Three resistors, A, B and C, are connected as shown in Figure. Each of them dissipates energy and can withstand a maximum power of 18W without melting. Find the maximum current that can flow through the three resistors? Image Three 2 Ω Resistors, a, B and C, Are Connected

Maximum current through resistor

Thus the maximum current through resistors B and C each

Question 21:

Should the resistance of an ammeter be low or high? Give reason should the resistance of an ammeter be low or high.

It should be as close to zero as possible. Ideally it should be zero ohm. If it is non-zero and substantial it will affect the true current.

Question 22:

Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of in series with a combination of two resistors (each) in parallel and a voltmeter across theparallel combination. Will the potential difference across the resistor be the same as that across the parallel combination of resistors? Give reason.

The circuit is shown as the figure:

Effective resistance of combination of two resistors (4 ohms each) in parallel is

Since, the resistor of 2 ohms and parallel combination of two 4 ohms resistors are in series, same current will flow through these. Hence, the potential difference across 2 ohms resistor is same as that across combination of two resistors.

Question 23:

How does use of a fuse wire protect electrical appliances?