Electric Current (Physics) Part-I

Total Questions: 50

31. Filament of electric bulb is made of: [Uttarakhand P.C.S. (Pre) 2012]

Correct Answer: (a) Tungsten
Solution:

Tungsten metal is used as filament in lighting bulbs. In 1781, Carl Wilhelm Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing tungsten acid.

Two years later in 1783, Juan Jose and Fausto Elhuyar were the first to isolate tungsten through the reduction of this acid with charcoal.

For this reason, they are credited with the discovery of this element. It's melting point is 3422°C and it's boiling point is 5555°C.

32. Consider the following statements: [I.A.S. (Pre) 1999]

An ordinary light bulb has a rather short life because the:

1. Filament wire is not uniform.

2. Bulb cannot be evacuated completely.

3. Wires supporting the filament melt at high temperatures.

Which of the above statements are correct?

Correct Answer: (d) 1, 2 and 3
Solution:

An ordinary light bulb has a rather short life because the:-

(1) Filament wire is not uniform (2) bulb cannot be evacuated completely and (3) wires supporting the filament melt at high temperature.

33. The temperature of the filament of lighted electric bulb is generally: [R.A.S/R.T.S. (Pre) 2007]

Correct Answer: (c) 2000°C to 2500°C
Solution:

Tungsten metal is used as filament in electric bulb. When electric current flows through it, its temperature goes up to 1500°C to 2500°C Generally, electric bulbs convert only 5% to 10% of electric energy into light.

34. Lightning can even burn a tree because it contains tremendous amount of [M.P.P.C.S. (Pre) 2017]

Correct Answer: (b) Electric energy
Solution:

Lightning can even burn a tree because it contains tremendous amount of electrical energy. Lightning is an electrical discharge caused by imbalance between storm clouds and the ground, or within the clouds themselves.

35. Consider the following statements: [Uttarakhand P.C.S.(Mains) 2002, U.P.P.C.S. (Pre) 1999]

Assertion (A): Lightning conductors prevent buildings from damages in the event of lightning strike.

Reason (R): The electric charge conduct to ground through the wire, instead of passing through the structure.

Select the correct answer using the codes given below:

Code:

Correct Answer: (a) Both (A) and (R) are correct, and (R) is the correct explanation of (A).
Solution:

A lightning conductor is a metal rod mounted on the top of an elevated structure, electrically bonded using a wire or electrical conductor to interface with ground through an electrode, engineered to protect the structure in the event of lightning strike.

If lightning hits the structure, it will preferentially strike the rod and would be conducted to ground through wire instead of passing through the structure, Hence the building will be saved by using this lighting conductor.

36. In a three-pin electrical plug longest pin should be connected to [U.P.P.C.S. (Pre) 2007]

Correct Answer: (a) Ground terminal
Solution:

In the three-pin plug, there are three ends namely live, neutral and earth. The earth pin on a plug is longer than the line and neutral pins.

This means the earth pin is the first to connect and last to disconnect for safety of electrical device. It provides an alternative and easy path for leakage or fault current flow.

37. In electric apparatus 'earth' is used: [U.P.P.C.S. (Pre) 2002]

Correct Answer: (c) For safety
Solution:

In the three-pin plug, there are three ends namely live, neutral and earth. The earth pin on a plug is longer than the line and neutral pins.

This means the earth pin is the first to connect and last to disconnect for safety of electrical device. It provides an alternative and easy path for leakage or fault current flow.

38. The electric current does not flow between two properly connected charged bodies if they are having [U.P.P.S.C. (R.I.) 2014]

Correct Answer: (d) Same potential
Solution:

According to Ohm's law, if there is a potential difference (V) across a resistor then there is a current (I) flowing through it. Current flows in a circuit as a result of difference in potential between two points in the circuit.

39. A fuse is used in main electric supply as a safety device. Which one of the following statements about the fuse is correct? [I.A.S. (Pre) 1998]

Correct Answer: (c) It must have a low melting point
Solution:

An electric fuse is a safety device used to prevent damage to an electrical circuit when excessive current flows through it. The electric fuse works on the principle of the heating effect of electric current.

It consists of a piece of wire made of a metal or an alloy of low melting point. As the current increases beyond a limit, the wire in the electric fuse melts and breaks off.

The fuse is then said to have blown off. The circuit is broken and current stop flowing through it. Thus, a fuse prevents fires.

40. Principle of fuse is [43ʳᵈ B.P.S.C. (Pre) 1999]

Correct Answer: (c) Heating effect of electricity
Solution:

An electric fuse is a safety device used to prevent damage to an electrical circuit when excessive current flows through it. The electric fuse works on the principle of the heating effect of electric current.

It consists of a piece of wire made of a metal or an alloy of low melting point. As the current increases beyond a limit, the wire in the electric fuse melts and breaks off.

The fuse is then said to have blown off. The circuit is broken and current stop flowing through it. Thus, a fuse prevents fires.