# Homework Help: Polytropic process

1. Nov 8, 2006

### Tux9876

Hi,

I have a question relating to a polytropic process. The question consists of two parts.

It says that the pressure (p) and the volume (v) of a gas undergoing a polytropic process are related by the equation:

p1V1^n = p2V2^n (where P1, P2 etc are individual variables as i dont know how to put sub text into the question)
the question then says...where n is the polytropic index.

IF

p1V1/T1 = p2V2/T2

determine an expression for p!, in terms of p2,T1,T2 and n

I have had a look on the net for help in answering the question but not luck so far.

2. Nov 9, 2006

### FredGarvin

I am assuming that you want to find P1 and not P factorial. This should be basic algebra (I hope). It looks like it could be a bit of a trick question because usually you just deal with P and V in a polytropic compression. To calculate T you need to know about the substance.

If $$P_1 V_1^n = P_2 V_2^n$$ Then

$$\frac{P_1 V_1}{T_1}=\frac{P_2 V_2}{T_2}$$

$$\frac{P_1 V_1^n}{T_1}=\frac{P_2 V_2^n}{T_2}$$

$$P_1 = \frac{P_2 T_1}{T_2} \left[ \frac{V_2}{V_1} \right] ^n$$

Last edited: Nov 9, 2006