Lesson_1.3_Printable_PPT

Lesson_1.3_Printable_PPT - First Law of Thermodynamics. The...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
First Law of Thermodynamics. The first law of thermodynamics is a statement of the law of conservation of energy that describes the behavior of systems when heat is either added or removed from them. Heat added to a system can result in two things: 1. It increases the internal energy of the system ( U ) . results in the system doing work ( Q = U + W 2. It results in the system doing work ( W ) If Q is the quantity of heat added to a system, then:
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This statement of the first law of thermodynamics establishes a direct relationship between heat and mechanical work. This statement suggests that mechanical energy can be converted to work and vice versa. While W is a measure of the work done by the system, -W is a measure of the work done on the system.
Background image of page 2
The internal energy U is a function of the state of the system, just as P, V and T are functions of the state of the system. When a gas is compressed for example, its states namely, P, V, T and U will all change. For a small quantity of heat dQ added to dQ = dU + dW system, the law can be stated as:
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Example 1 : If 1.68 x 10 6 J of heat energy is added to a gas that expands and does 800 kJ of work, what is the change in the internal energy of the gas? dQ = 1.68 × 10 6 J dW = 8.0 × 10 5 J dQ = dU + dW dU = dQ – dW = 1.68 × 10 6 – 8.0 × 10 5 = 8.8 × 10 5 J
Background image of page 4
Example 2: At Niagara falls, the water drops 50 m. If the change in potential energy goes into internal energy of the water, compute the increase in its temperature. U = mgh Let us consider m kg of water at the top of the fall. Its potential energy U = mgh. Potential energy at the bottom is U = 0 U = 0 The change in energy U = mgh U = mgh
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
U = mgh If ∆θ is the change in temperature of water, its increase in internal heat energy is: dQ = m c w ∆θ ∆θ This change in energy becomes internal heat energy. = mgh h .8 50 U = 0 U = mgh w gh C θ ∆ = 9.8 50 4180 × = = 0.12 K
Background image of page 6
A lead bullet initially at 30 o C just melts upon striking a target. Assuming that all of the initial kinetic energy of the bullet goes into the internal energy of the bullet to raise its temperature and melt it, calculate the speed of the bullet upon impact. (Melting point of lead is 327 o C and L f for lead is 2.47 x 10 4 J.kg -1 , specific heat of lead c L = 128 Jkg -1 K -1 et the speed of the bullet be nd its mass . Let the speed of the bullet be v and its mass m. The kinetic energy
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 28

Lesson_1.3_Printable_PPT - First Law of Thermodynamics. The...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online