NCERT Book Class 10 Science Lab Manual How Things Work

How Things Work

MATERIALS REQUIRED

A resistor of about 5 Ω, an ammeter ( 0 - 3 A), a voltmeter (0 - 10 V), four dry cells of 1.5 V each with a cell holder (or a battery eliminator), a plug key, connecting wires, and a piece of sand paper.

PROCEDURE

1. Note the range and least count of the given ammeter and the voltmeter.

2. Fresh connecting wires have an insulating layer on it. Similarly the connecting wires lying unused for some time may also develop an insulating layer. (How?) It is therefore important to clean the ends of connecting wires using a sand paper.

3. Draw a circuit diagram for studying the Ohm’s law as shown in Fig. 48.1 in your notebook. Observe how different components like the ammeter, voltmeter, resistor, and the plug key are connected with the cells (or battery eliminator).

4. Set up the circuit by connecting different components with the help of connecting wires. Initially connect only one cell in the circuit (that is make cell connections between points A and B). In case a battery eleminator is used, keep the rating of the eliminator at the minimum (say at 2 V).

5. Make sure that the positive and negative terminals of the ammeter and voltmeter are correctly connected in the circuit as shown in Fig. 48.1. Get the circuit set up by you checked by the teacher, before inserting the key into the plug.

6. Insert the key in the plug to let the current establish in the circuit. Note the readings of the ammeter and voltmeter and record them. The voltmeter measures the potential difference (V) across the two ends X and Y of the resistor, and the ammeter measures the current I through it. Remove the key from the plug to avoid unnecessary heating of wires. (How does it happen? Think it in accordance with the Joule’s law of heating.)

7. Now instead of using one cell in the circuit, connect two cells in the circuit (that is make cell connections between points A and C, in case a battery eliminator is used, increase its rating. Insert the key in the circuit. Note and record the voltmeter and ammeter readings.

8. Repeat the experiment by connecting three and four cells in the circuit.

QUESTIONS

a. In this experiment it is advised to take out the key from the plug when the observations are not being taken. Why?

b• Suppose the ammeter (or voltmeter) you are using in this experiment do not have positive (+) and negative (-) terminal markings. How will you use such ammeter (or voltmeter) in the circuit?

c• If the resistor of a known resistance value is replaced with a nichrome wire of 10 cm length (say). How do the values of current through the nichrome wire and potential difference across the two ends of it may change? How the values will change if the replaced wire is of manganin in place of nichrome?

d• Suppose in this experiment you see that the deflection on ammeter (or voltmeter) scale goes beyond the full scale. What will you infer from such an observation? What will you infer if the deflection takes place in opposite direction?

e• Why is it advised to clean the ends of connecting wires before connecting them?

f• What do you conclude if no deflection in the galvanometer is observed in this experiment?

g• Explain different ways to induce current in a conducting coil.

h• A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) inserted into the coil, (ii) pulled out from the coil, and (iii) held stationary inside the coil.

i• Two current-carrying coils 1 and 2 are placed closed to each other. If the current in the coil 1 is changed, will there be some induced current in the coil 2? Why?

j• Name the devices which are based on the phenomenon of electromagnetic induction.

Please refer to attached file for NCERT Class 10 Science Lab Manual How Things Work