Physics - Study Mode

[#1141] The frequency of direct current is ________
Correct Answer

(A) Zero

Explanation

Solution: The frequency of direct current (DC) is 0 Hz, as the current only flows in one direction.

[#1142] Resistance of human body in dry condition
Correct Answer

(D) 100000 ohm

Explanation

Solution: The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 ohms.

[#1143] The purpose of choke in a fluorescent lamp is :
Correct Answer

(B) To decrease the current flow

Explanation

Solution: The choke primarily serves to limit current flow to the correct level for the tube. It also can be used during startup to provide an inductive ‘kick’ forming a momentary higher-voltage pulse to start the lamp.

[#1144] An electron and a proton starting from rest get accelerated through potential difference of 100 kV. The final speed of the electron and the proton are Ve and Vp respectively. Which of the following relations is correct?
Correct Answer

(A) Ve > Vp

Explanation

Solution: Both when accelerated through a potential difference of 100 kV, they will have the same energy. The mass of the electron is less than the mass of a proton, hence it will move faster(momentum).

[#1145] Superconductors are those elements
Correct Answer

(B) Whose resistance falls almost to zero at very low temperatures

Explanation

Solution: Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source.