A point charge 20.0 nC is located at the center of a cube whose sides are of length 10.0 cm. If there is no other charges in thi
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Answer:
The work function ϕ of the metal = 53.4196 x 10⁻¹⁶ J
Explanation:
When light is incident on a photoelectric material like metal, photoelectrons are emitted from the surface of the metal. This process is called photoelectric effect.
The relationship between the maximum kinetic energy () of the photoelectrons to the frequency of the absorbed photons (f) and the threshold frequency (f₀) of the photoemissive metal surface is:
= h(f − f₀)
= hf - hf₀
E is the energy of the absorbed photons: E = hf
ϕ is the work function of the surface: ϕ = hf₀
= E - ϕ
Frequency f = 8.12×10¹⁸ Hz
Maximum kinetic energy = 4.16×10⁻¹⁷ J
Speed of light c = 3 x 10⁸ m/s
Planck's constant h = 6.63 × 10⁻³⁴ Js
E = hf = 6.63 × 10⁻³⁴ x 8.12×10¹⁸
E = 53.8356 x 10⁻¹⁶ J
from = E - ϕ ;
ϕ = E -
ϕ = 53.8356 x 10⁻¹⁶ - 4.16×10⁻¹⁷
ϕ = 53.4196 x 10⁻¹⁶ J
The work function of the metal ϕ = 53.4196 x 10⁻¹⁶ J
(a)
Wien's displacement law is summarized by the equation
where
is the peak wavelength
is Wien's displacement constant
T is the absolute temperature at the surface of the star
For an O-type star, we have
T = 40,000 K
Therefore, its peak wavelength is
(b) Ultraviolet
We can answer this part by looking at the wavelength range of the different parts of the electromagnetic spectrum:
gamma rays
X-rays 1 nm - 1 pm
ultraviolet 380 nm - 1 nm
visible light 750 nm - 380 nm
infrared
microwaves 1 mm -
radio waves > 1 mm
The peak wavelength of this star is
Therefore, it falls in the ultraviolet region.
(c) No
The Keck telescopes is actually a system of 2 telescopes in the Keck Observatory, located in Mauna kea, Hawai.
The two telescopes, thanks to several instruments, are able to detect much of the electromagnetic radiation in the visible ligth and infrared parts of the spectrum. However, they are not able to detect light in the ultraviolet region: therefore, they cannot observe the star mentioned in the previous part of the problem.