A copper ball 2 cm in radius is heated in a furnace to 327 °C. If its emissivity is 0.3, at what rate does it radiate energy?
1.72 W
2.73 W
11.0 W
2.15 W
Young's modulus for a steel wire is 2 x 1011 Pa and its elastic limit is 2.5 x 108 Pa. By how much can a steel wire 3 m long and 2 mm in diameter be stretched before the elastic limit is exceeded?
3.75 mm
7.50 mm
4.75 mm
4.00 mm
A.
3.75 mm
The cross-sectional area of a wire of radius r = l mm= 10-3m is A = = 3.14 x 10-6 m2.
The maximum force that can be applied without exceeding the elastic limit is therefore
F =
F = (2.5 × 108 N m-2 ) ( 3.14 × 10-6 m2 )
F = 785 N
When this force is applied, the wire will stretch by
ΔL =
=
= 3.75 × 10-3 m
ΔL = 3.75 mm
Assertion: In an isolated system the entropy increases.
Reason: The process in an isolated system is adiabatic only.
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Assertion: The fundamental frequency of an open organ pipe increases as the temperature is increased.
Reason: This is because as the temperature increases, the velocity of sound increases more rapidly than length of the pipe.
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
Assertion: A hollow metallic closed container with small opening maintained at a high temperature can act as a source of black body radiation.
Reason: All metals act as black body radiator.
If both assertion and reason are true and reason is the correct explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
If assertion is true but reason is false.
If both assertion and reason are false.
The force per unit length between two straight conductors separated by a distance of 0.02 m is 2 x 10-3 N m-1. The current in one conductor is 10 A and that in the other conductor is
20 A
5 A
2 A
10 A
What is the magnetic field on the axis of a coil of radius r carrying current I at a distance R from the origin?
The temperature of transition from ferromagnetic property to paramagnetic property is called
Transition temperature
Critical temperature
Curie temperature
Triplet temperature