Experiment E8 (S1): Frequency of a Tuning Fork by Melde’s Experiment
Q1: What is a stationary wave? Ans: A stationary wave is the effect of the superposition of two sets of identical progressive waves (waves having the same amplitude and time period) but traveling in opposite directions with the same velocity. This is a case where very often occurs with stationary sound waves.
Q2: How are the stationary waves formed in Melde’s Experiment? Ans: Stationary waves are produced due to the superposition of the direct waves sent by the tuning fork and waves reflected from the pulley.
Q3: How the transverse arrangements differ from a longitudinal arrangement? Ans:
- In the longitudinal mode of vibration, the fork and the string vibrate in the same direction but in case of transverse mode of vibration, the tuning fork and the string are set into perpendicular direction.
Q4: What are the modes in which a string can vibrate? Ans: There are two modes in which a tuning fork vibrates. The modes are longitudinal and transverse.
Q5: How the tension in the longitudinal arrangement differ from that in the transverse arrangement? Ans: The tension in the longitudinal arrangement will be one-fourth of that in the transverse arrangement.
Q6: Why the length of the string between the pulley and the scale pan should be kept short? Ans: Otherwise, the approximate mass of this portion of the string will increase the tension of the string.
Q7: Can you perform your experiment with a thick wire? Ans: The rigidity of the wire in addition to its tension will have a controlling force and the simple formula employed may not hold well.
Q8: What are nodes and antinodes? Ans: (See Figure in the source) Nodes are points which are permanently at rest while are the antinodes at which the medium swings to and fro with the maximum extent. At the nodes, displacement is , velocity is , and the change of density is maximum.
Q9: How do you know that resonance has occurred between the fork and the string? Ans: When the amplitude of vibration of the antinodes is greatest, we know that the desired resonance has occurred.
Q10: Why do the loops in the central part of the thread should be counted for measurements? Ans: The loops in the central part of the thread should be counted for measurements. The nodes at the tip of the prong and at the pulley should be neglected as these have some motion.
Experiment E20 (MD1): Photoelectric Effect
Q1: What is Photoelectric Effect? Ans: The photoelectric effect is a phenomenon in physics based on the idea that electromagnetic radiation is made of particles called photons. When a photon hits an electron on a metal surface, the electron can be emitted.
Q2: What do you mean by photoelectric work function? Ans: The photoelectric work function is the minimum photon energy required to liberate an electron from a substance in the photoelectric effect.
Q3: What is Planck’s law of radiation? Ans: Planck’s law is a formula for the spectral radiance of an object at a given temperature as a function of frequency () or wavelength (). It has dimensions of power per solid angle per area per frequency/power per solid angle per area per wavelength.
Q4: What is Photoelectric cell? Ans: A photoelectric cell, also called Electric Eye, Photocell, or Phototube, is an electron tube with a photosensitive cathode that emits electrons when illuminated. It works on the principle of the photo-electric effect and converts light energy into electrical energy.
Q5: Which photons have more energy, those in blue light or those in red light? Ans: Shorter waves vibrate at higher frequencies and have higher energies. Blue light has a higher frequency () and higher energy () than red light (, ).
Q6: How does the intensity of light affect the photoelectric effect? Ans: The number of electrons ejected (the electric current) is proportional to the intensity. The current is independent of the frequency of the incident radiation above the threshold value ().
Q7: What does the photoelectric effect show about the properties of light? Ans: It shows that light, when observed, forces a surface to release electrons when the light hits. Einstein explained this by defining light as a stream of photons, or energy packets.
Q8: What are the Characteristics of Photoelectric Effect? Ans: Photo-electrons are emitted only when the frequency of incident light is greater than or equal to a certain minimum frequency () known as the threshold frequency.
Q9: What is stopping potential? Ans: The stopping potential is the potential necessary to stop any electron from reaching the other side. It is a measure of the maximum kinetic energy of the electrons emitted as a result of the photoelectric effect.
Q10: What is photoconductivity? Ans: Photoconductivity is an increase in the electrical conductivity of a nonmetallic solid when exposed to electromagnetic radiation.