A crystal diffracts a beam of electrons, like a 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?
(a) 0.18 nm
(b) 48 V
You might also like to view...
An object moves in a circle of radius R at constant speed with a period T. If you want to change only the period in order to cut the object's acceleration in half, the new period should be
A) T/4. B) T/2. C) T/ . D) T . E) 4T.
A 51 g steel ball is released from rest and falls vertically onto a steel plate. The ball strikes the plate and is in contact with it for 0.5 ms. The ball rebounds elastically, and returns to its original height
The time interval for a round trip is 3.00 s. In this situation, the average force exerted on the ball during contact with the plate is closest to: A) 3,000 N B) 1,500 N C) 2,490 N D) 2,000 N E) 3,500 N
A 0.3-cm-thick aluminum plate has rectangular fins 0.16 x 0.6 cm, on one side, spaced 0.6 cm apart. The finned side is in contact with low pressure air at 38°C and the average heat transfer coefficient is 28.4 W/(m2 K). On the unfinned side water flows at 93°C and the heat transfer coefficient is 284 W/(m2 K). (a) Calculate the efficiency of the fins (b) calculate the rate of heat transfer per unit area of wall and (c) comment on the design if the water and air were interchanged.
GIVEN
FIND
(a) The fin efficiency (?f)
(b) Rate of heat transfer per unit wall area (q/Aw)
(c) Comment on the design if the water and air were interchanged
ASSUMPTIONS
Width of fins is much longer than their thickness
The system has reached steady state
The thermal conductivity of the aluminum is constant
SKETCH
If a current of 2.4 A is flowing in a wire of diameter 2.0 mm, what is the average current density?
A) 7.6 × 105 A/m2 B) 5.2 × 10-6 A/m2 C) 1.9 × 105 A/m2 D) 3.6 × 105 A/m2 E) 21 × 10-6 A/m2