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
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?
A.
Consider a circular coil of radius r, carrying a current I. Consider a point P, which is at a distance X from the centre of the coil. We can consider that the loop is made up of a large number of short elements, generating small magnetic fields. So the total field at P will be the sum of the contributions from all these elements. At the centre of the coil the field will be uniform. As the location of the point increases from the centre of the coil, the field decreases.
By Biot-Savart's law, the field dB due to a small element 'dl' of the circle, centred at A is given by
dB =
This can be resolved into two components, one along the axis OP, ad other PS, which is perpendicular to OP. Ps get cancelled with PS'. So the magnetic field at a distance x away from the axis of circular coil of radius r is given by
Bx =
The temperature of transition from ferromagnetic property to paramagnetic property is called
Transition temperature
Critical temperature
Curie temperature
Triplet temperature