MHB Multiple choices question on specific heats of gases

AI Thread Summary
In the discussion, two cylinders containing an ideal diatomic gas are analyzed, with one cylinder having a movable piston and the other a fixed piston. When equal amounts of heat are added, the temperature rise in the movable piston cylinder (A) is 30 K, while the fixed piston cylinder (B) experiences a different temperature change. The relationship between specific heats at constant pressure and volume is highlighted, with the ratio for diatomic gases being 1.4. The calculations show that the temperature rise in cylinder B is 42 K, confirming the initial answer provided. The discussion emphasizes the importance of understanding specific heat in relation to temperature changes in gases.
WMDhamnekar
MHB
Messages
376
Reaction score
28
Two cylinders A and B fitted with pistons contain equal amounts of an ideal diatomic gas at 300 K. 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) 18 K
(C) 50 K
(D) 42 K

My answer is 42 K. Is this answer correct?
 
Mathematics news on Phys.org
Okay, what do YOU understand about this problem? You titled it "specific heat" so you must know that specific heat has something to do with this. How is specific heat of a gas related to its temperature?
 
Country Boy said:
Okay, what do YOU understand about this problem? You titled it "specific heat" so you must know that specific heat has something to do with this. How is specific heat of a gas related to its temperature?
The piston in the cylinder A is free to move. Hence pressure of the gas is constant and the heat is given to it at constant pressure. that means $ Q_A=nC_p \Delta T_A$ where,
Q is the heat supplied or needed to bring about a change in temperature ($\Delta T$) in 1 mole of a substance ;
n is the amount of gas in moles;
$C_p$ is the molar heat capacity of a body of given substance at constant pressure.

The piston of the cylinder B is fixed. Hence the volume of the gas is constant and the heat is given at constant volume i.e., $ Q_B= nC_v \Delta T_B$ where $C_v$ is the molar heat capacity of a body of substance at constant volume.
The ratio of specific heats for a diatomic gas is $\frac{C_p}{C_v}=\frac75=1.4$. The heat given to the two gases are equal, $Q_A =Q_B$
So,
$\Delta T_B = \frac{C_p}{C_v}\Delta T_A= 42 K$
 
Looks good to me.
 
Seemingly by some mathematical coincidence, a hexagon of sides 2,2,7,7, 11, and 11 can be inscribed in a circle of radius 7. The other day I saw a math problem on line, which they said came from a Polish Olympiad, where you compute the length x of the 3rd side which is the same as the radius, so that the sides of length 2,x, and 11 are inscribed on the arc of a semi-circle. The law of cosines applied twice gives the answer for x of exactly 7, but the arithmetic is so complex that the...
Back
Top