Bakelite is used in making electrical appliances because it is a

• good conductor of heat

• good conductor of electricity

• good insulator of electricity

• thermoplastic

When electric current is passed through a metallic conductor, amount of heat produced in the conductor depends on its

• material and thickness

• material, length and thickness

• material and length

• length and thickness

Anjali asks the following tasks to be performed by students of Class VII while making an electromagnet (not in correct sequence).
(i) Place some pins near the end of a nail.
(ii) Switch on the current and observe what
(iii) Wind a copper 'wire tightly around an iron nail.
(iv) Connect free end of the wire to the terminals of a cell.
Which one of the following is the correct sequence of task to be performed to achieve the desired result?

• (i), (ii), (iii), (iv)

• (iii), (iv), (i), (ii)

• (iii), (i), (ii), (iv)

• (iv), (ii), (iii), (i)

Which is significant for a fuse wire?

• Its melting point

• Its specific resistance

• Current flowing through it

• All of the above

Which one of the following elements is a donor impurity?

• Al

• B

• Ga

• P

Which among the following liquids are conductors of electricity?

1. Vinegar
2. Sugar solution
3. Salt solution
4. Distilled water

• A, C and D

• B and C

• A and C

• C and D

17.

Which of the following facts is not correct about magnets?

• The attraction is a sure test of magnetism

• Magnetic field lines originate from North-pole and merge at South-pole of a magnet

• Like poles of a magnet repel each other

• The magnetic field is stronger at the poles of a bar magnet

Magnetic quantum number determines

• shape of orbitals

• orientation of orbitals

• total energy of an-orbital

• spin of an electron

Three-wire of resistance 1Ω, 2Ω, and 3Ω respectively are connected in 'parallel'. The equivalent resistance of the circuit is

• $\frac{6}{11}\mathrm{\Omega }$

• $\frac{11}{6}\mathrm{\Omega }$

• 6Ω

• $\frac{1}{6}\mathrm{\Omega }$

The relation between the speed of sound (v) and absolute temperature (T) in gas is

• v ∝ T

• $\mathrm{v} \propto \sqrt{\mathrm{T}}$

• $\mathrm{v} \propto \frac{1}{\mathrm{T}}$

• $\mathrm{v} \propto \frac{1}{\sqrt{\mathrm{T}}}$