Important points for Science Exam CBSE Board 2024

Electricity and Magnetic effect of current

 1. A voltmeter has a high resistance so that it takes a negligible current from the circuit.

2. An ammeter should have very low resistance so that it may not change the value of the current flowing in the circuit.

3. According to Ohm's law, "At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its end".

4. Factors affecting the resistance of a conductor:

(i) Length of the conductor

(ii) Area of cross section of the conductor

(iii) nature of the material of the conductor

(iv) temperature of the conductor.

5.The SI unit of resistivity is Ohm meter.

6. Advantage of parallel Circuits in Domestic wiring:

(i) The overall resistance of household circuits is reduced due to which the current from the power supply is high.

(ii) If one electrical appliance stops working due to some defect, then all other appliances keep working normally.

(iii) Each electrical appliance has its own switch due to which it can be turned on or turned off independently, without affecting other appliances.

(iv) Each electrical appliance gets the same voltage.

7. The south pole of earth's magnet is in the geographical north  because it attracts the north pole of the suspended magnet.

8. Similarly, the north pole of earth's magnet is in the geographical south because it attracts the south pole of the suspended magnet.

9. Solenoid: The solenoid is long coil containing a large number of close turns of insulated copper wire.

10. Electric fuse: A fuse is a safety device having a short length of a thin, tin plated copper wire having low melting point, which melts and breaks the circuit if the current exceeds a safe value.

An electric fuse works on the Heating effect of current.

A fuse wire is connected in series in the electric circuits.

A pure copper wire cannot be used as a fuse wire.

MCBs work on the magnetic effect of current.