When Deepak studied the electrical circuits and the current flowing through them, he became curious about the range of the currents we come across in daily life. He collected the data and presented in a tabular form as shown below. He then studied the instruments used to detect and measure current, however, could not understand the difference between an ammeter and an ideal ammeter and thus went to his teacher for the explanation.

(i) What values did Deepak have?

(ii) As domestic appliances carry an electric current of the order of few amperes, write one safety precaution we should take while working with them.

(iii) An ammeter of resistance RA is connected in series with a resistor R and a battery of emf E and internal resistance r. The current flowing through this circuit is IA. What will be the current flowing through the circuit if the given ammeter is replaced by an ideal ammeter and find the percentage error in measuring the current through an ammeter?

(i) Deepak had values of Curiosity to gain knowledge, Intelligence, Awareness and Passion for learning as he inquired about something he studied theoretically and wanted to gain practical knowledge about the subject and its application in real life.

(ii) Domestic appliances generally carry currents of the order of few amperes, but they can be hazardous too so precaution must be kept while working with them, like

(a) Wearing Shoes or slippers (made of proper insulating materials like rubber leather etc.) which will break the circuit between our body and ground, so even one accidentally touch a high voltage source current will not flow through his body to the ground as the circuit is broken

(b) Preferably use Rubber Gloves while working so that Person’s body is properly insulated from the current source.

(c) Never touch any appliance with a wet hand as water is a good conductor of electricity and it will increase chances of Person getting an electric shock.

(iii) Ammeter is a device Used to measure Electric current in a circuit, it is connected in series combination as current across all the elements connected in series is same, an ammeter should have really low resistance so that it does not affect the resistance of original circuit, hence not distorting the original values to be measured, an ideal ammeter is one which is assumed to have no resistance, i.e. 0 Resistance, so it does not affect the circuit even a bit . the circuit diagram of an Ammeter connected with a resistance and a battery is shown below

Here an Ammeter of resistance RA is connected in series with a resistance R and battery of emf E and internal Resistance R

Now we know according to Ohm's law, the potential difference across a resistor is equal to the product of current flowing through it and its Resistance Mathematically,

V = IR’

Where V is the potential difference across the ends of the register, I is the current flowing through it and R’ is the resistance

Alternatively, we can find the current in the circuit as

I = V/R.’

Where V is the potential difference applied across the circuit with net resistance R.’

Now here net resistance of the circuit will be the sum of three components as all are connected in series

So net resistance of the circuit is

R’ = R + R_A + r

Net Voltage across circuit will be the voltage applied by battery i.e.

V = E

So current in the circuit will be

So ammeter will also measure this much amount of current

If this ammeter is replaced by an ideal ammeter, i.e. one with no internal resistance or we can say

R_A = 0

The current flowing in the circuit would be

In practical case, no ammeter is ideal and have some internal resistance, so there is always some error in measurement, so percentage error in the measurement of current through ammeter is

So putting the value of I and I’ we get

Ammeter resistance is very less as compared to original resistance of the circuit so neglecting RA in the denominator we get

So percentage error depends on the ratio of ammeter resistance to original resistance of the circuit.