16 of 20 You want to increase the efficiency of a Carnot engine by changing the

Question

16 of 20

You want to increase the efficiency of a Carnot engine by changing the temperature of either its hot or cold reservoir by the same number of degrees ?T. Which of the following choices will produce the greater increase in its thermodynamic efficiency?

Question

17 of 20

The thermal efficiency equation e = W/Qw is valid for which of the following heat engines?

Question

18 of 20

At what approximate distance from a particle with a charge of 5.00 (nC) does the electric field of that charge have a magnitude of 4.00 N/C?

Question

19 of 20

A 9.6-?C point charge is at the center of a cube with sides of length 0.500 m. What is the electric flux through one face of the cube?

Question

20 of 20

A -5.00-nC point charge is on the x axis at x = 1.20 m. A second point charge Q is on the x axis at -0.600 m. If the resultant electric field at the origin is 45.0 N/C in the + x direction, what is the sign and magnitude of charge Q?

a Increase the temperature of the hot reservoir by ?T b Decrease the temperature of the cold reservoir by ?T c Decrease the temperature of the hot reservoir by ?T d Increase the temperature of the cold reservoir by ?T e It would not matter. The increase in efficiency would be the same for all choices since ?T is the same.

Explanation / Answer

16) Efficiency eta = 1-(Tc/Th)

if Th increases Tc/Th decreases
If Tc/Th increases then eta also increses
So the required answer is a)    Increase the temperature of the hot reservoir by ?T

17) that is appicable tp all types of heat engines

so answer is d) All types of heat engines

18) E = k*q/r^2

E = 4 N/C

q = 5*10^-9 C

k = 9*10^9

r = sqrt(k*q/E)= sqrt((9*10^9*5*10^-9)/(4))

r= 3.35 m = 3.4 m

So teh correct answer is b) 3.4 m

19) Elctric flux = q/(6*eo) = (9.6*10^-6)/(6*8.85*10^-12) = 180790.96 = 1.80E5 N-m2/C

so the correct answer is d) 1.80E5 N-m2/C

20) E = E1+E2

E1 = k*q/x1^2 = (9*10^9*5*10^-9)/(1.2^2) = 31.25 N/C

E2 = 45-31.25 = 13.75 N/C

but E2 = k*Q/x2^2

13.75 = (9*10^9*Q)/(0.6^2)

Q = 0.55 nC and positive sign

So answer is C) +5.5*10^-10 C

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