An ammeter with a scale ranging from 0 to 15mA has a resistance of 5Ω . How should the instrument be connected with a resistor (and with what resistance) to measure: (a) current of 0 to 0.15A, (b) a potential difference from 0 to 150V?

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\frac{5}{9} Ω, 9995 Ω

\frac{5}{8} Ω, 9995 Ω

\frac{5}{11} Ω, 9995 Ω

\frac{5}{12} Ω, 9995 Ω

answer is A.

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Detailed Solution

Concept- Understanding the connection of resistors in which voltage or current is constant is necessary to answer this topic. In the first scenario, we must identify the resistor that will allow us to adjust the current's range. In contrast, in the second scenario, we need to identify the resistor that will allow us to adjust the voltage range. We will do this by connecting resistors in parallel and in series.
To measure a current of 0 to, in case a, we must determine the kind of connection and the quantity of resistance to link with the instrument.

. Since the voltage won't change, we know that the current can fluctuate. If the resistor is linked in parallel with the instruments, this is feasible. Therefore, let's assume that the instrument is linked in parallel with a resistor. We'll travel

and

For parallel connection of resistors,

Thus, our answer for case

is: The resistance of

should be connected in parallel with the instrument.
Now, in case b, we need to find the type of connection and amount of resistance to be connected with the instrument to measure a potential difference from 0 to

.
The variation in voltage will be done if the resistor is connected in series.
Let us take

and

We know that for series connection,

Thus, our answer for case B is: The resistance of

should be connected in series with the instrument.
Hence, the correct option is 1.

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