Physics Lab Experiments: Electricity and Magnetism
Activity: Magnetic Field Near Current-Carrying Conductor
To observe the deflection of a magnetic needle placed near a conductor carrying current.
Apparatus and Materials:
Magnetic needle, battery, ammeter, rheostat, key, conducting wire, etc.
Theory:
When electric current passes through a conductor, a magnetic field is produced around it.
Procedure:
- Remove magnetic substances from the table and place the magnetic needle on it. Connect the cell, rheostat, key, and ammeter in series with the experimental wire as shown in Fig. 37. Place the wire XY above the needle in the same direction on two blocks of thermocol.
- Close the key (K), adjust the rheostat so that current flows through the circuit. Take the ammeter reading. Observe the magnitude and direction of deflection of the needle.
Observation:
Table of deflections of the magnetic needle:
| No. Of Observation | Ammeter Reading | Magnitude and Direction of Deflection of N Pole |
|---|---|---|
| 1, 2, 3 | … division left | |
| After changing the Direction of Current (1, 2, 3) |
Conclusion:
A magnetic field is produced near a current-carrying conductor. The direction and intensity of the field depend on the direction and magnitude of current flowing through the conductor.
Activity: Multimeter Usage and Circuit Continuity Check
To measure resistance, voltage (AC/DC), current (AC), and check the continuity of a given circuit using a multimeter.
Apparatus and Materials:
A multimeter, carbon resistance of different values.
Theory:
A multimeter can measure AC as well as direct current and AC as well as direct voltage in addition to resistance. For this purpose, its panel is divided into five different sections. The section and the range within one section can be changed by rotating a knob.
Checking Continuity of a Circuit:
- Turn the multimeter knob to the ohmmeter range of the least value. Touch the ends of the two leads with each other and adjust the pointer to zero reading to show full-scale deflection.
- Place and press the two ends of the leads at the points between which the continuity of the circuit is to be tested. A full-scale deflection of the pointer indicates the continuity of the circuit.
Observation:
1) Table for Measurement of Resistance
| Resistor | Colour Code Rings (1, 2, 3, 4) | Value of Tolerance | Resistance from Multimeter | Difference in % |
|---|---|---|---|---|
| R1 | ||||
| R2 | ||||
| R3 | ||||
| R4 |
2) Table for Measurement of DC and AC Voltage:
| DC or AC Voltage | Voltage Between Terminals | Voltage Measured By Multimeter V (volt) | Difference V – V° (volt) |
|---|---|---|---|
| DC | |||
| AC |
Conclusion:
- Within the tolerance limits, the decoded values of resistors tally with the values measured by the multimeter.
- DC and AC voltages marked on the sources match with the voltages measured by the multimeter.
Activity: Assembling a Household Circuit
Object: To assemble a household circuit comprising of three bulbs, three on-off switches, a fuse, and a power source.
Apparatus and Materials:
Three bulbs (25 W, 40 W and 60 W), three on-off switches, a fuse wire, a two-pin plug, flexible red and black PVC connecting wires, a board with a two-pin socket and main switch.
Procedure:
- Connect one end of the bulb holder to the red flexible wire through a switch in series. Connect the other end of the holder to the black flexible wire.
- Connect the three bulb-switch combinations in parallel: red wire ends at one point, and black wire ends at the other points.
Testing:
Turn the switches on one by one and then turn them off one by one.
Observations:
The bulb glows when the switch is made on. It stops glowing when the switch is put off.
Precaution:
The fuse wire should be suitably selected.
Activity: Analyzing and Correcting an Electric Circuit Diagram
Object: To draw the diagram of a given open circuit comprising at least a battery, rheostat, key, ammeter, and voltmeter. To mark the components that are not connected in proper order and correct the circuit and the circuit diagram.
Apparatus and Materials:
Battery, Rheostat, ammeter, voltmeter, resistance box, key, connecting wires, etc.
Theory:
A cell is said to be in an open circuit when no current is drawn from it. In a closed circuit, the cell is connected in series with the key, rheostat, and ammeter. The voltmeter is connected in parallel with the resistance box.
Procedure:
- Connect the given components as shown in the initial figure (assumed Fig. 40).
- In Fig. 41, the ammeter (A) is connected in parallel to the rheostat, and the voltmeter (V) is connected in series with the cell. So, these are not connected in proper order, and hence, the circuit is wrong.
- In Fig. 42, the ammeter (A) is connected in series with the cell, while the voltmeter (V) is connected in parallel to the resistance box (R). The two components are connected in proper order, and hence, the circuit diagram is correct.
- Insert the plug in key K, take some resistance out from the resistance box, and adjust the rheostat. The ammeter and voltmeter show readings.
- Take the plug out, keeping the key open. The ammeter and voltmeter show zero reading. The circuit is open now.
Conclusion:
Components in an electric circuit should be connected in the proper order.