Question

An amplifier has an input signal of 5V at 0.1mA. The output of the amplifier provides 10mA to a 450Ω load
determine : a) the current , voltage and power gains
b) the input resistance to the amplifier

Answer 1

Explanations & Calculations

• Input current = 0.1mA
• Output current = 10mA
• Output voltage = $\small 10mA \times450 \Omega = 4.5V$

• Therefore, current gain = $\large \frac{10mA}{0.1mA} \small = \bold{100}$
• Voltage gain = $\large \frac{4.5V}{5V} \small = \bold{0.9}$

• Power gain = $\large \frac{\text{output power}}{\text{input power}} \small = \large \frac{4.5V\times 10mA }{5V \times 0.1mA} \small =\bold{90}$

• Input resistance = $\large \frac{\text{input voltage}}{\text{input current}} = \frac{5V}{0.1mA} \small =\bold{50k \Omega}$