Which equation best expresses the first law of thermodynamics, assuming q is heat, u is internal energy, and w is work?

a.δw= δq+ δu

b.δw= δu − δq

c.δq= δu+w

d.δu=q −w

The first law of thermodynamics is expresses by

D. ΔU=Q-W

which means change in internal energy of system = Heat added to system minus work done by the system

All are expressed in Joules.

This law is based on principle of conservation of energy.

(d) is the correct option ''''

Explanation:

The first law of thermodynamics states the law of conservation of energy i. e. heat energy can neither be created nor be destroyed. The mathematical expression that show the first law of thermodynamics is as follows:

Where

is the change in internal energy

Q is the amount if heat added to the system

W is the work done by the system

Hence, the correct option is (d)

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.