Case Study Questions Class 12 Physics Chapter 9 Ray Optics and Optical Instruments
CBSE Class 12 Case Study Questions Physics Ray Optics and Optical Instruments. Term 2 Important Case Study Questions for Class 12 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Ray Optics and Optical Instruments.
At Case Study Questions there will given a Paragraph. In where some Important Questions will made on that respective Case Based Study. There will various types of marks will given 1 marks, 2 marks, 3 marks, 4 marks.
CBSE Case Study Questions Class 12 Physics Ray Optics and Optical Instruments
Case study 1:
As we know that, when light ray travels from one medium to another changes its direction of path due to the change in optical density of the medium. When light ray travels from optically denser medium to the optically rarer medium then some of the light get reflected back in the same medium and remaining light get refracted in the second medium and such a phenomenon of light is called as internal reflector light. We know that, when a ray of light travels from denser medium to rarer medium then it get bended away from the normal. If we increase the angle of incidence slowly then angle of refraction also get increased and at one stage the angle of refraction is 90° for some angle of incidence. And further if we increase the angle of incidence then there will be no refraction of light and the ray will be totally internally get reflected. Such phenomenon of reflection of light is called as total internal reflection of light. And the angle of incidence in denser medium for which the angle of refraction in rarer medium is 90°, that angle of incidence is called as critical angle. So we define total internal reflection as, if the angle of incidence exceeds the critical angle then the total light get internally reflected. Mirage is the best real life example of total internal reflection of light. The highly brilliance of diamonds is only due to the total internal reflection of light through them which is get total internally reflected many times and causes brilliance of diamonds. Prisms are also made by using total internal reflection of light. We all know that, optics is the vast branch of physics which has vast application in our daily life such as optical fibre. Optical fibre are used for long distance transmission of audio and video signal also. And they are mainly constructed on the basis of total internal reflection of light to reduce the decrease in amplitude of the sending signal.
Questions:
Q 1.) For critical angle the value of corresponding angle of refraction is____
a) 180°
b) less than 90°
c) greater than 90°
d) 90°
Q 2.) As the refractive index of the medium increases the corresponding value of critical angle for that medium ____
a) decreases
b) increases
c) remains same
d) independent of refractive index of the medium
Q 3.) In case of total internal reflection, for angle of incidence greater than critical angle the refraction of light is not possible because____
a) Snell’s law of refraction get satisfied
b) Snell’s law of refraction cannot be satisfied
c) laws of refraction cannot be satisfied
d) can’t say
Q 4.) What is mean by optically denser and optically rarer medium?
Q 5.) How total internal reflection of light would be possible in case of optical fibres?
Answer key:
Q 1.) d) 90°
Q 2.) a) decreases
Q 3.) b) Snell’s law of refraction cannot be satisfied
Q 4.) Optical density is not related to mass density of the medium. Optical density is the simply ratio of speed of light in two media. Optical density of the medium depends on the refractive index of the medium mainly. More is the refractive index of the medium greater is the optical density and such medium is called as optically denser medium.
Lower is the refractive index of the medium then lower it’s optical density also. Such medium with lower refractive index is called as optically rarer medium. While speed of light is higher in rarer medium than the speed of light in denser medium.
Q 5.) Optical fibres are used mainly for long distance transmission of signals. They are made up of high quality composite glass or quartz fibres which consists of core and cladding. The refractive index of core is higher than the cladding. So core acts as a rarer medium and cladding acts as the denser medium. The signal in the form of light is sended from one end of the fibre at a particular angel of incidence so that the light must get totally internally reflected. In such way, light get totally internally reflected many times along the length of the fibre and finally will be received at the other end without loss in intensity. In this way, by total internal reflection of light the long distance signal transmission is possible through optical fibres.
Case study 2:
We all know that, the different colours of light are due to the different wavelength or frequency of light. The visible spectrum shows different colours from which red light is having longer wavelength and violet light is having shortest wavelength. As the wavelength of the light increases the corresponding refractive index of the medium decreases. Because that glass is dispersive medium while vacuum is not. As the speed of light depends on the refractive index and there by on the wavelength also. So it is responsible for the desperation of light in that medium. We see in rainy season, after raining there is a rainbow in the sky which is only due to the dispersion of sunlight through water droplets present in the atmosphere. The observer can see the rainbow when he is seeing opposite to the direction where sun is present. The blue colour of the sky is due to the scattering of light by the atmospheric dust particles. Light having shorter wavelength scatters more than the light having longer wavelength. Hence, violet light having shorter wavelength get scattered more than blue light but the light reaches to our eyes is blue mostly. Because our eyes cannot be sensitive to violet light. The sun looks reddish at sunset and sunrise only because of the scattering of light. The red light having longer wavelength get scattered less and directly reach to our eyes while other light having greater wavelength get scattered more and doesn’t reach to our eyes that’s why we see the sun as reddish in colour at sunset and sunrise near the horizon.
Questions:
Q 1.) The formation of rainbow in the sky is because of____
a) dispersion of light
b) refraction and reflection of light
c) scattering of light
d) both a and b
Q 2.) The amount of scattering of light is inversely proportional to the fourth power of its____
a) frequency
b) wavelength
c) refractive index
d) speed of light
Q 3.) Red light scatters less because it’s wavelength is____
a) longer
b) less
c) both a and b
d) can’t say
Q 4.) Why vacuum acts as a non dispersive medium?
Q 5.) Which colour having longest and shortest wavelengths give the corresponding values of wavelengths?
Answer key:
Q 1.) d) both a and b
Q 2.) b) wavelength
Q 3.) a) longer
Q 4.) As we know that, the optical properties of the medium depends on the refractive index of the medium, speed of light in that medium also. In vacuum the speed of light is constant and it is independent of the wavelength also. So all light colours travels with the same speed due to which there will be no dispersion and hence vacuum acts as the non dispersive medium. Hence, sunlight reaching to us is also in the form of white light only.
Q 5.) In visible light spectrum, the red colour is having longer wavelength and which is near about 700nm while the violet light colour is having shortest wavelength which is about 400nm. Longer is the wavelength less will be scattering and hence red light scatters less than violet light.