Question

A student in the lab has 3 resistors in which one is 8 ohm and two of 4 ohm , one ammeter and battery of 12 V. He wants that ammeter to show the maximum reading for current from cell. Draw the circuit and calculate current.

Answer 1

connect all resistor in parallel connection.

so it's equivalent resistor= 1.6ohm
so I =12/1.6 = 7.5 A

Answer 2

The maximum current reading is 7.5A.

Step-by-step explanation:

Given: 3 resistors of readings-  8Ω, 4Ω, and 4Ω, one ammeter and battery of 12V

To find:  maximum current reading in the ammeter.

Since, current is inversely proportional to resistance, for maximum current we need to have minimum resistance.

This is possible for a combination in which all resistors are in parallel.

Equivalent resistance for Parallel Combination is found by:

$\frac{1}{R_{eq} } = \frac{1}{R1} +\frac{1}{R2} +...\frac{1}{Rn}$

Using this formula, we get:

$\frac{1}{R_{eq} } = \frac{1}{8} +\frac{1}{4} +\frac{1}{4}$

     $=\frac{5}{8}$

∴$R_{eq} = 1.6$Ω

Calculation of Current :

$I=\frac{V}{R_{eq} }$

∴$I=\frac{12}{1.6}$

   $=7.5A$

Hence, the maximum current reading from the ammeter is 7.5A.

The circuit diagram is as shown :