Draw a simple circuit of a CE transistor amplifier. Explain its working. Show that the voltage gain AV, of the amplifier is given by , where is the current gain, RL is the load resistance and ri is the input resistance of the transistor. What is the significance of the negative sign in the expression for the voltage gain?
Circuit diagram of CE transistor amplifier,
When an ac input signal VI (to be amplified) is superimposed on the bias VBB, the output, which is measured between collector and ground, increases.
We first assume that Vi = 0.
Applying Kirchoff’s law to the output loop,
VCC = VCE + IC RL
Similarly, the input loop gives,
VBB = VBE + IB RB
When Vi is not zero, we have
VBE + Vi = VBE + IB RB +
Change in IB causes changes in Ic
The change in VCE is the output voltage Vo is,
The voltage gain of the amplifier is,
Negative sign in the expression shows the output voltage and input voltage have phase difference of .
Define magnifying power of a telescope. Write its expression.
A small telescope has an objective lens of focal length 150 cm and an eye piece of focal length 5 cm. If this telescope is used to view a 100 m high tower 3 km away, find the height of the final image when it is formed 25 cm away from the eye piece.
a) Magnifying power of telescope is the ratio of the angle subtended at the eye by the image to the angle subtended at the unaided eye by the object.
Mathematically, we can write
where, fo is the focal length of the objective, fe is the focal length of the eye-piece and D is the least distance of distinct vision.
b) Using, the lens equation for objective lens,
Hence, magnification due to the objective lens is given by,
Now, using lens formula for eye-piece, we get
Therefore, magnification due to eyepiece me =
Hence, total magnification,
So, size of final image =
Draw the circuit diagram of a full wave rectifier using p-n junction diode. Explain its working and show the output, input waveforms.
(b) Show the output waveforms (Y) for the following inputs A and B of(i) OR gate
b) Output waveforms for the following inputs A and B of OR gate and NAND gate.