AmplifierAn amplifier increases the strength of an electrical signal.

Symbol:

Type: analogue process device

Amplifiers are used in:1. radios and TV’s2. intercoms3. baby alarms

Amplifiers increase the amplitude of the electrical signal.

FREQUENCY is NOT CHANGED.

Voltage Gain

Vi Vo

LARGER AMPLITUDEFREQUENCY stays the SAME

input signal

output signal

The size of the voltage gain is given by:i

ogain V

VV

x

÷Vo

Vgain Vi

Quantity UnitOutput Voltage ( Vo )

Voltage Gain ( Vgain )

Input Voltage ( Vi )

Volts ( V )

NO UNIT

Volts ( V )

The voltage gain of an amplifier is the number that the input voltage is multiplied by to give the output voltage.

Example 1An amplifier turns a 20 mV signal into 300 mV signal.Calculate the voltage gain of the amplifier.

mV 20Vi

mV 300Vo

?Vgain

i

ogain V

VV

3-

-3

102010300

15Vgain ** NO UNIT **

V 1020 -3

V 10300 -3

V 0.02

V 0.3

Example 2An amplifier with a voltage gain of 80 is supplied with an input voltage of 7 mV.Calculate the output voltage.

mV7 Vi

?Vo

80Vgain igaino VVV

-310780

V 0.56Vo V 107 -3 V0.007

Power GainThe power gain of an amplifier is given by:

i

ogain P

PP

x

÷Po

Pgain Pi

Quantity UnitOutput Power ( Po )

Power Gain ( Pgain )

Input Power ( Pi )

Watts ( W )

NO UNIT

Watts ( W )

There are also 3 formulae for electrical power we met in the topic “Using Electricity”

V IP

R IP 2

RVP

2

x

÷P

I V

x

÷P

I2 R

x

÷V2

P R

Example 1An amplifier has an output power of 50 W.The input voltage is 12 V and the input resistance is 1 kΩ.Calculate: (a) the input power

(b) the power gain.

V 12Vi

kΩ 1Ri Ω 101 3

?Pi

RVP

2

3

2

10112

Ω 1000

W 0.144P

(CREDIT)

(a)

(b)W 0.144Pi

W 50Po

?Pgain

i

ogain P

PP

0.14450

347Pgain ** NO UNIT **

Yellow BookPage 56

Analogue Processes – Q63Voltage Gain –Q67, Q70

Page 57Power, Voltage, Resistance – Q72, Q73

Power Gain – Q76

Yellow BookMixed Problems on Amplifiers

Q80, Q84, Q86, Q88