## Monday, October 12, 2009

### IIT JEE Physics Final Revision Set 42

1. The half life of 131I is 8 days. Given a sample of 131I at time t = 0, we can assert that:
(A) no nucleus will decay before t = 4 days
(B) no nucleus will decay before t = 8 days
(C) all nuclei will decay before t = 16 days
(D) a given nucleus may decay at any time after t = 0

2. Two identical containers A and B with frictionless pistons contain the same ideal gas at the same temperature and the same volume V. The mass of the gas in A is mA and that in B is mB. The gas in each cylinder is now allowed to expand isothermally to the same final volume 2V. The changes in the pressure in A and B are found to be DP and 1.5 DP respectively. Then :
(A) 4 mA = 9mB (B) 2mA = 3mB
(C) 3mA = 2mB (D) 9mA= 4mB

3. A given quantity of an ideal gas is at pressure P and absolute temperature T. The isothermal bulk modulus of the gas is:
(A) 2/3 P (B) P
(C) 3/2 P (D) 2P

4. Two cylinders A and B fitted with pistons contain equal amounts of an ideal diatomic gas at 300K. The piston of A is free to move, while that of B is held fixed. The same amount of heat is given to the gas in each cylinder. If the rise in temperature of the gas in A is 30 K, then the rise in temperature of the gas in B is:
(A) 30 K (B) 18K
(C) 50 K (D) 42 K

5. A concave mirror is placed on a horizontal table with its axis directed vertically upwards. Let 0 be the pole of the mirror and C its centre of curvature. A point object is placed at C. It has a real image, also located at C. If the mirror is now filled with water, the image will be:
(A) real and will remain at C
(B) real and located at a point between C and ยต
(C) virtual and located at a point between C and 0
(D) real and located at a point between C and 0

Source 1998 JEE