Author Question: A solid concrete wall has dimensions 4.0 m 2.4 m and is 30 cm thick. The thermal conductivity of ... (Read 88 times)

K@ · **on:** Jul 29, 2018

A solid concrete wall has dimensions 4.0 m 2.4 m and is 30 cm thick. The thermal conductivity of the concrete is 1.3 W/m K,

and it separates a basement from the ground outside. The inner surface of the wall is at 18C, and the outside surface is at 6C. How much heat flows through the wall every hour?
A) 1.8 MJ
B) 1.8 kJ
C) 500 J
D) 5.0 MJ
E) 5.0 kJ

Question 2

A crystal diffracts a beam of electrons, like a diffraction grating, as they hit it perpendicular to its surface.

The crystal spacing is 0.18 nm, and the first maximum scattering occurs at 80 relative to the normal to the surface. (e = 1.60 10-19 C, melectron = 9.11 10-13 kg, h = 6.626 10-34 J s)
(a) What is the wavelength of the electrons?
(b) What potential difference accelerated the electrons if they started from rest?