One person says that the potentil energy of a particular book kept in an almirah is 20 J and the other says it is 30J. Is one of them necessarily wrong?

Two neutral particles are kept 1m apart. Suppose by some mechanism some charge is transferred from one particle to the other and the electric potential energy lost is completely converted into a photon. Calculate the longest and the next smaller wavelength of the photon possible. h=6.63xx10^(-34)Js .

A hat contains a number of cards with 30% white on both sides, 50% black on one side and whit e on the other side, 20% black on both sides. The cards are mixed up, and a single card is drawn at random and placed on the table. Its upper side shows up black. The probability that its other side is also black is 2//9 b. 4//9 c. 2//3 d. 2//7

Take three different colour sheets , place one over the other and draw a triangle on the top sheet. Cut the sheets to get triangles of different colour which are identical. Mark the vertices and the angles as shown. Place the interior angles angle1,angle2 and angle3 on a straight line, adjacent to each other, without leaving any gap. What can you say about the total measure of the three angles angle1,angle2 and angle3 ? Can you use the same figure to explain the ''Exterior angle property'' of a triangle ? If a side of a triangle is stretched, the exterior angle so formed is equal to the sum of the two remote interior angles.

A silver ball of radius 4.8 cm is suspended by a thread in a vacuum chamber, Ultraviolet light of wavelength 200nm is incident on the ball for some time during which a total light energy of 1.0 xx 10^-7 J falls on the surface. Assuming that on the average one photon out of every ten thousand is able to eject a photoelectron, find the electric potential at the surface of the ball assuming zero potential at infinity. What is the potential at the centre of the ball?

Two discharge tubes have identical material structure and the same gas is filled in them. The length of one tube is 10cm and that of th other tube is 20cm. Sparking starts in both the tubes when the potential difference between the cathode and the anode is 100 V . If the pressure in the shorter tube is 1.0 mm of mercury, what is the pressure in the longer tube?

One end of a rod length 20cm is inserted in a furnace at 800K. The sides of the rod are covered with an insulating material and the other end emits radiation like a blackbody. The temperature of this end is 750K in the steady state. The temperature of the surrounding air is 300K. Assuming radiation to be the only important mode of energy transfer between the surrounding and the open end of the rod, find the thermal conductivity of the rod. Stefan constant sigma=6.0xx10^(-1)Wm^(-2)K^(-4) .

In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas. If the initial internal energy of the gas was 30 J , what will be the final internal energy ?

One number is greater than the thrice the other number by 2. If 4 j times the smaller number exceeds the greater by 5. find the number.

A string of linear mass density 0.5 g cm^-1 and a total length 30 cm is tied to a fixed wall at one end and to a frictionless ring at the other end. The ring can move on a vertical rod. A wave pulse is produced on the string which moves towards the ring at a speed of 20 cm s^-1 . The pulse is symmetric about its maximum which is located at a distance of 20 cm from the end joined to the ring. (a) Assuming that the wave is reflected from the ends without loss of energy, find the time taken by the string to regain its shape. (b) The shape of the string changes periodically with time. Find this time period. (c) What is the tension in the string ?

An aluminium rod and a copper rod of equal length 1.0 m and cross-sectional area. 1cm^(2) are welded together as shown in figure. One end is kept at a temperature of 20^(@)C and the other at 60^(@)C Calculate the amount of heat taken out per second from the hot end. thermal conductivity of aluminium =200Wm^(-1)C^(-1) and of copper =390Wm^(-1)C^(-1) .