Quick Review Flashcards - Click to flip and test your knowledge!
Question
In a triangular prism, what is the formula for the total angle of deviation $\delta$ for a light ray?
Answer
$\delta = \delta_1 + \delta_2$
Question
The angle of deviation $\delta_1$ at the first surface of a prism depends on the angle of incidence and the _____ of glass with respect to air.
Answer
refractive index
Question
Identify three factors upon which the total angle of deviation $\delta$ of a prism depends.
Answer
Angle of incidence ($i$), angle of the prism ($A$), and refractive index of the material ($\mu$).
Question
How does the speed of light in a transparent medium change as the wavelength of light decreases?
Answer
The speed of light decreases.
Question
What is the relationship between the refractive index of glass and the wavelength of incident light?
Answer
The refractive index increases as the wavelength decreases.
Question
In visible light, which colour is deviated the most by a triangular prism?
Answer
Violet
Question
In visible light, which colour is deviated the least by a triangular prism?
Answer
Red
Question
Why is violet light deviated more than red light when passing through glass?
Answer
Violet light has a lower speed in glass, leading to a higher refractive index and greater deviation.
Question
Term: Wavelength
Answer
Definition: The characteristic of light that determines its colour, independent of its origin.
Question
What is the approximate wavelength range of violet light in Angstroms ($\text{\AA}$)?
Answer
$4000 \text{ \AA}$ to $4460 \text{ \AA}$
Question
What is the approximate wavelength range of red light in Angstroms ($\text{\AA}$)?
Answer
$6200 \text{ \AA}$ to $8000 \text{ \AA}$
Question
Convert $1$ nanometre ($\text{nm}$) into Angstroms ($\text{\AA}$).
Answer
$1 \text{ nm} = 10 \text{ \AA}$
Question
Which visible colour has the highest frequency in the spectrum?
Answer
Violet
Question
Which visible colour has the lowest frequency in the spectrum?
Answer
Red
Question
What is the frequency range of visible light in units of $10^{14} \text{ Hz}$?
Answer
$3.75 \times 10^{14} \text{ Hz}$ to $7.5 \times 10^{14} \text{ Hz}$
Question
Term: Dispersion
Answer
Definition: The phenomenon of splitting white light by a prism into its constituent colours.
Question
Term: Spectrum
Answer
Definition: The band of colours seen on a screen after white light passes through a prism.
Question
What is the fundamental cause of the dispersion of white light in a medium?
Answer
Different wavelengths of light travel at different speeds in the medium.
Question
At which surface of a prism does the dispersion (splitting) of white light occur?
Answer
The first surface
Question
At which surface(s) of a prism does the deviation of light rays occur?
Answer
Both the first and second surfaces
Question
State the order of colours in the visible spectrum starting from the base of the prism.
Answer
Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR).
Question
What did Sir Isaac Newton conclude about the nature of white light from his prism experiment?
Answer
White light is polychromatic, consisting of a mixture of several colours.
Question
True or False: A prism produces colours from within its own material.
Answer
False, it only splits the various colours already present in the incident light.
Question
Why is no spectrum visible when white light passes through a parallel-sided glass slab?
Answer
The emergent rays of different colours are parallel and too close to be distinguished as separate.
Question
When a beam of red, blue, and yellow light is incident normally on a prism face, why do they pass without deviation at that first surface?
Answer
The angle of incidence is $0^\circ$ ($i = 0^\circ$).
Question
In an isosceles right-angled glass prism ($n = 1.5$), which visible colour typically undergoes total internal reflection at the hypotenuse face if $i = 45^\circ$?
Answer
Blue (because its critical angle is less than $45^\circ$).
Question
What formula relates frequency ($f$), wavelength ($\lambda$), and the speed of light ($c$)?
Answer
$c = f \lambda$
Question
Calculate the wavelength of light in nanometres if its frequency is $7.5 \times 10^{14} \text{ Hz}$ and $c = 3 \times 10^8 \text{ m s}^{-1}$.
Answer
$400 \text{ nm}$
Question
The part of the electromagnetic spectrum with wavelengths shorter than violet light is called the _____.
Answer
invisible spectrum
Question
Arrange these EM radiations in order of increasing wavelength: X-rays, Radio waves, Visible light, Infrared.
Answer
X-rays, Visible light, Infrared, Radio waves.
Question
Which radiations in the electromagnetic spectrum have the shortest wavelengths?
Answer
Gamma rays
Question
Which radiations in the electromagnetic spectrum have the longest wavelengths?
Answer
Radio waves
Question
State the wavelength range for X-rays in Angstroms ($\text{\AA}$).
Answer
$0.1 \text{ \AA}$ to $100 \text{ \AA}$
Question
State the wavelength range for Ultraviolet radiations in Angstroms ($\text{\AA}$).
Answer
$100 \text{ \AA}$ to $4000 \text{ \AA}$
Question
State the wavelength range for Infrared radiations in Angstroms ($\text{\AA}$).
Answer
$8000 \text{ \AA}$ to $10^7 \text{ \AA}$ (or $1 \text{ mm}$)
Question
What is the speed of all electromagnetic waves in a vacuum?
Answer
$3 \times 10^8 \text{ m s}^{-1}$
Question
Do electromagnetic waves require a material medium for propagation?
Answer
No
Question
What is the nature of electromagnetic waves in terms of their oscillation direction relative to propagation?
Answer
They are transverse waves.
Question
Are electromagnetic waves deflected by electric or magnetic fields?
Answer
No
Question
Which type of EM radiation is produced during the decay of radioactive nuclei?
Answer
Gamma rays
Question
Which EM radiations are used in radiotherapy to kill cancer cells?
Answer
Gamma rays
Question
How are X-rays produced in a laboratory setting?
Answer
By stopping a highly energetic electron beam with a heavy metal target of high melting point.
Question
Which property of X-rays allows them to be used for detecting bone fractures?
Answer
They can penetrate human flesh but are stopped by bones.
Question
Who first detected ultraviolet radiations in 1801?
Answer
Professor J. Ritter
Question
Why is a quartz prism used instead of a glass prism to obtain the ultraviolet spectrum?
Answer
Glass absorbs ultraviolet radiations, whereas quartz allows them to pass.
Question
Name a chemical solution used to detect ultraviolet radiations through its darkening effect.
Answer
Silver chloride solution
Question
What is a major harmful effect of long-term exposure to ultraviolet radiations on the human body?
Answer
Skin cancer
Question
Which layer in the Earth's atmosphere protects us by absorbing a large fraction of solar UV radiation?
Answer
The ozone layer
Question
Who first detected the infrared part of the spectrum in about 1800?
Answer
William Herschel
Question
Which instrument is commonly used to detect infrared radiations by their heating effect?
Answer
A thermopile (or a blackened bulb thermometer)
Question
Why is a rock-salt prism used to obtain the infrared spectrum instead of a glass prism?
Answer
Glass absorbs infrared radiations, while rock-salt does not.
Question
State a use of infrared radiations in medicine.
Answer
Therapeutic purposes by doctors.
Question
Why are infrared radiations used for photography in fog or mist?
Answer
They are scattered less by the atmosphere due to their long wavelength, allowing them to penetrate deep.
Question
Which EM waves are used in radar communication and molecular structure analysis?
Answer
Microwaves
Question
Term: Scattering of light
Answer
Definition: The process of absorption and then re-emission of light energy by dust particles and air molecules.
Question
State Rayleigh's law regarding the intensity of scattered light ($I$) and its wavelength ($\lambda$).
Answer
$I \propto \frac{1}{\lambda^4}$
Question
According to Rayleigh's law, how much more is violet light scattered compared to red light?
Answer
Nearly 16 times more.
Question
Why does the sky appear blue to an observer on Earth?
Answer
Short-wavelength blue light is scattered much more by air molecules than longer-wavelength colours.
Question
Why does the Sun appear red during sunrise and sunset?
Answer
Light travels a long distance through the atmosphere; blue light is scattered away, leaving mostly red light to reach the eye.
Question
What colour would the sky appear to an astronaut in space where there is no atmosphere?
Answer
Black