Download physics experiments for class 12 students and more Essays (high school) Physics in PDF only on Docsity!
To Study The Variation in Potential Drop
With Length of a Wire For a Steady Current
Aim To study the variation in potential drop with length of a wire for a steady current. Apparatus and material Apparatus. Potentiometer: Material: A fully charged 4.5 V battery or battery eliminator, a low resistance rheostat, a voltmeter of range (0-3.0 V), an ammeter (0-3) A, a one way key, a jockey, a set square, connecting wires and a piece of sand paper. Theory For a potentiometer with wire of uniform material density and thickness (cross-sectional area) carrying a steady current, potential drop is proportional to the length of the wire. where K is the drop of potential per unit length. It is called the potential gradient. Diagram
Procedure
- Draw a circuit diagram showing the scheme of connections as in figure.
- Remove the insulation from the ends of the connecting copper wires with a sand paper.
- Connect the positive pole of the battery (eliminator) (a battery of constant e.m.f.) to the zero end (P) of the potentiometer and the negative pole through a one-way key, an ammeter and a low resistance rheostat to the other end (Q) of the potentiometer.
- Connect the positive terminal of the voltmeter to the end P of the potentiometer and the negative terminal to the jockey.
- Touch the end of the jockey to the end Q of the potentiometer.
- Close the key and set the rheostat such that the voltmeter gives full scale deflection (3 V).
- Touch the jockey at end P at 0 (zero) cm. The voltmeter will give zero deflection.
- Touch the jockey at marks separated by 50 cm length of wire. Note the voltmeter reading in each case.
- Record your observations in tabular form as given ahead. Observations and Calculations
To use a multimeter to (a) identify base of
transistor, (b) distinguish between npn and
pnp type transistors, (c) see the
unidirectional flow of current in case of a
diode and an LED, (d) check whether a
given electronic component (e.g., diode,
transistor or IC) is in working order
Aim To use a multimeter to: (a) identify base of transistor (b) distinguish between npn and pnp type transistors. (c) see the unidirectional flow of current in case of a diode and an LED. (d) check whether a given electronic component (e.g., diode, transistor or IC) is in working order. Apparatus A multimeter, transistors, npn and pnp, an IC (integrated circuit 7408 or 7432 each with 14 legs), a diode and an LED. Theory
- A transistor is a three terminal device. It can be regarded as a combination of two junction diode joined in an opposite manner such that the middle part is common to both. When an n-type of semi-conductor is sandwitched between two p-type of semiconductors, the transistor is p-n-p type but when p-type of semi-conductor, the transistor is npn transistor. Input section is forward biased and output section of a transistor is reversed biased. The base current is small but emitter and collector current is large. Ic = Ib + Ic. (a) Identify the base: If one of the three terminals of the transistor is so chosen that conduction take place in both the cases when a multimeter is connected between the chosen terminal and either of the remaining two terminals, then the chosen terminal is the base. (b) To find out whether the transistor is p-n-p or n-p-n: For conduction to be possible in both the above said cases, if the common terminal of the transistor has to be connected to +ve, then the transistor is n-p-n type. But if the common terminal has to be connected to -ve for making the conduction possible in both the case, then
the transistor is p-n-p type. (c) Identifying an IC. An IC has minimum of eight legs. Most of the IC packages have flat back. (d) A diode or an LED conducts only when forward biased and in reverse biasing, there is no flow of current. (e) When a diode is in working order, it will allow the current to flow in one direction, when forward biased. Procedure
- Use the selector switch and put the multimeter in ohm range (R).
- Insert the metallic end of the back lead in common terminal of the multimeter and that of the red in the terminal marked P.
(a)A high resistance would mean 3 and 1 are both n-type and 2 is p-type the base. (b) A low resistance would mean a forward biasing of 3 and 1 (i.e., 3 is n, 1 is p and 2 is p). It means base is 3 and the transistor is p-n-p type.
Identifying the emitter and collector leads (Having known the base). In
a transistor, the emitter region is heavily doped relative to the collector
region. Therefore, the forward resistance of emitter base should be lower
than that of collector base. Using ohm-meter (multimeter set at R) the
forward resistance of the lead with base having lower value implies that the
lead is Emitter and the other offering higher forward with base is the
collector.
When reverse biased, a diode does not conduct. An LED behaves the
same way except that a diode when conducts emits light.
A transistor conducts only when base-emitter is forward biased and does
not conduct when base-collector is forward biased.
(c) IC (integrated circuit). Look for number of legs of the device. Eight or
more than eight legs imply that the component is an IC.
(d) Unidirectional flow of current
Case of junction diode
1. Connect the +ve marked end of the diode to +ve terminal of a 6 V
variable D.C. battery adjusted to minimum voltage.
2. Select the D.C. current at 10 mA range by using the selector switch.
Insert one the metallic ends of probe in terminal P(+) and the black
metallic end into the ter¬minal marked common.
3. Connect the other metallize end of red probe to the free end of the
diode and the metallic end of black probe into the -ve terminal of the
battery eliminator and read the value of current by varying the output
of the eliminator. Since the diode is forward biased, it allows the
current to pass.
4. Now reverse the terminals of the diode such that the end marked -ve
is at higher potential* and the one marked + is at lower potential.
Again observe the current in multimeter on the appropriate D.C.
milliampere scale. No current reading in the multimeter would indicate
that the diode allows the flow of current in one direction only, i.e., the
current is unidirectional in a diode.
5. Now replace the diode by the LED and repeat the steps to establish
that an LED also allows the flow of current only when it is forward
biased as well as emits light.
(e) Checking whether diode, transistor in IC is in working order
1. A diode will conduct only in one direction i.e., first connect the ends of
diode to the two metal ends of the probes and reverse the connecting
points. If it conducts in one case, then diode is in working order. If
conducts in both cases or does not conduct in both cases, then it is
damaged.
To Assemble The Components of a Given
Electrical Circuit
Aim
To assemble the components of a given electrical circuit.
Apparatus and material
Apparatus: A voltmeter and an ammeter of appropriate range, a battery, a
rheostat, one way key.
Material: An unknown resistance or resistance coil, connecting wires, a
piece of sand paper.
Diagram
Procedure
1. Connect the components (Resistors, inductors etc.) in series with each
other as shown in diagram and then in series with the battery.
2. Connect the ammeter in series with the circuit, to measure the current.
3. Connect the voltmeter in parallel to the resistor, to measure the
potential difference.
4. Connect the switch in series with the battery.
5. Assembly of the electrical components in electric circuit is complete.
Utility
It is used for measuring an unknown resistance (see Experiment 2 :
Section A).
