Quantum Physics

Question 12:Amin conducted an experiment to determine the work function and threshold wavelength for a material X. The arrangement of the apparatus is as shown in Figure 2.When the cathode coated with material X is illuminated by a light beam of wavelength, λ, the emitted photoelectrons will move towards the anode and give a reading … Read more

Question 11:When a photodiode is shone on with a red light (λ = 700 nm) and a blue light (λ = 400 nm), the maximum kinetic energy of the photoelectrons emitted by the blue light is two times that of the red light.(a) What is the work function of the photodiode?(b) What is the threshold … Read more

Question 9:Figure 1 shows a photocell constructed using semiconductor material that can be activated by a light with a maximum wavelength of 1 110 nm.(a) What is the threshold frequency and work function of the semiconductor?(b) Why does the semiconductor look opaque at room temperature?Answer:(a)$$ \begin{aligned} f_0 & =\frac{c}{\lambda_0} \\ & =\frac{3.00 \times 10^8}{1110 \times … Read more

Question 8:Complete Table 1 with information on the wavelength and photon energy for several components of waves in the electromagnetic spectrum.Answer:$$ \begin{aligned} E & =\frac{h c}{\lambda} \\ & =\frac{\left(6.63 \times 10^{-34}\right)\left(3.00 \times 10^8\right)}{500 \times 10^{-9}} \\ & =3.98 \times 10^{-19} \mathrm{~J} \\ & =\frac{3.98 \times 10^{-19} \mathrm{~J}}{1.60 \times 10^{-19} \mathrm{~J}} \\ & =2.5 \mathrm{eV} \end{aligned} … Read more

Question 6:(a) Why is a large cavity with a small hole able to act as a black body?(b) The temperature of a black body is 4500 K and it looks orange-yellow. Describe the colour changes in the black body as the body is heated to a temperature of 9000 K.Answer:(a)The rays of light that enter … Read more

Question 4:A laser light beam with a wavelength of 555 nm and a power of 5.00 mW is aimed at an object without any light reflected. Calculate: (a) the momentum of a photon in the laser beam(b) the number of photons per second in the laser light beam hitting the objectAnswer:(a)$$ \begin{aligned} \text { Momentum … Read more

Question 1:State the meaning of the following terms:(a) black body(b) quantum of energyAnswer:(a) A black body is an ideal body that is able to absorb all the electromagnetic rays that fall on it.(b) Quantum of energy is a discrete packet of energy and not a continuous energy. Question 2:The minimum energy required for the photoelectron … Read more

Question 1:(a) State Einstein’s Photoelectric Equation.(b) State the meaning of:(i) work function(ii) threshold frequency(iii) the relationship between work function and threshold frequencyAnswer: (a)$$ h f=W+\frac{1}{2} m v^2 \text { max } $$(b)(i)Work function, W is the minimum energy required for a photoelectron to be emitted from a metal surface.(b)(ii)Threshold frequency, f0 is the minimum frequency … Read more

Question 1:What is meant by photoelectric effect?Answer:Emission of electrons from a metal surface when shone on by light of a certain frequency. Question 2:Will a bright light emit more photoelectrons from a metal surface compared to a dim light of the same frequency?Answer:Yes. The number of photoelectrons emitted depends on the number of photons that … Read more

Question 1:What is the frequency and energy of a photon with a wavelength of 10 nm?Answer:Speed of light in vacuum , c = 3.00 × 108 m s-1Wavelength, λ = 10 nm= 10 × 10-9 m$$ \begin{aligned} &\text { Frequency, } f=\frac{c}{\lambda}\\ &\begin{aligned} & =\frac{3.00 \times 10^8}{10 \times 10^{-9}} \\ & =3.0 \times 10^{16} \mathrm{~Hz} … Read more