Question

What is the ammeter reading?

• A. 0.4
• B. 1
• C. 0.6
• D. 1.2

Answer 1

Answer: (B)

Components connected in parallel are connected so the same voltage is applied to each component. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component. To find the total resistance of all components, the reciprocals of the resistances of each component is added and the reciprocal of the sum is taken. Hence, the Total resistance will always be less than the value of the smallest resistance. That is, $\frac{1}{R_{total}}=\frac{1}{R_1}+\frac{1}{R_2}...\frac{1}{R_n},R={R_{total}}^{-1}$. . Components connected in series are connected along a single path, so the same current flows through all of the components. The current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component. In a series circuit, every device must function for the circuit to be complete. One bulb burning out in a series circuit breaks the circuit. A circuit composed solely of components connected in series is known as a series circuit.The total resistance of resistors in series is equal to the sum of their individual resistances. That is, $R_{total}=R_1+R_2...R_n$.
The resistances 10 ohms and 2 ohms in the upper half of the circuit are connected in series. So the combined resistance is R1 = 10 + 2 = 12 ohms.
The resistances 25 ohms and 5 ohms in the lower half of the circuit are connected in series. So the combined resistance is R2 = 25 + 5 = 30 ohms.
Now, the total resistance R in the circuit is R1 + R2 = $\frac{1}{12}+\frac{1}{30}=\frac{1}{0.11}=8.6ohms$ as they are connected in parallel.
The total current in the circuit is given as 1.4 A. So, the total voltage V = IR (Ohm's law) = $1.4\times 8.6=12.04V$.
The voltage remains the same across the circuit as it is a parallel connection. So, the current across the upper half of the circuit where the ammeter is connected is calculated as I = V/R = 12.04 (total voltage)/12(Resistance R1) = 1 A.
Hence, the ammeter will read 1 A.