|
|
Investigating Components having
Non-Linear Characteristics
| 1.
Preparation: |
a) |
Read
about diodes and voltage dependent resistors. You do NOT need to
know HOW they work but just how they behave in circuits. |
|
b) |
See expt 1EM for
circuit diagram. |
|
c) |
Parts 3 and 4 below. |
| 2. |
Obtain
results to plot the characteristics of
a) a 3·5v bulb
b) a voltage dependent resistor, v.d.r. (sometimes called a
varistor)
c) a silicon diode |
| 3. |
Using the
same circuit as experiment 1EM, connect the component to be
investigated first one way then the opposite way. Plot
your results on axes as shown below. Use a 6v d.c. supply for
the bulb and diode. Increase to 24v for the v.d.r. |
|
 |
|
|
IMPORTANT
Set the potential
divider to give zero voltage before
connecting the component into the circuit, then increase
the voltage very gradually.
For the bulb
you can safely go up to Imax
= 300mA.
For the diode, Imax
= 100mA.
For the v.d.r., Imax
= 10mA. |
|
| 4. |
Using the
Characteristics |
|
Consider the circuit shown
below, in which E = 1·1 V and r = 25
W.
(A diode connected as shown below is said to be "forward
biased".) |
|
 |
|
Try to calculate the current, I
which flows in the circuit and the voltage, V across the diode.
It will soon become clear that you can not calculate
these answers without knowing the detailed characteristics of
the diode (make sure you understand why this is the
case). Let us assume that the diode in this circuit is the one
which you used in your experiment. If you plot the characteristics
of the battery in this circuit on the same axes as the
characteristics of the diode, you should see how to answer the
questions. |
|
Using the same method, consider the following
circuit, in which the bulb is the one you used in your
experiment, E = 4·5 V and r = 15 W. |
|
 |
|
Find the voltage across the bulb and
the current flowing in the circuit. |
|
© David
Hoult 2008 |
The
Open Door Web Site