CBSE Class 12 Physics VBQs Ray Optics

Ray Optics

Question 1. Ravi is using yellow light in a single silt diffraction experiment with silt width of 0.6 mm. The teacher has replaces yellow light by x-rays. Now he is not able to observe the diffraction pattern. He feels sad. Again the teacher replaces x-rays by yellow light and the diffraction pattern appears again. The teacher now explains the facts about the diffraction and

• Which value is displayed by the teacher?

• Give the necessary condition for the diffraction.

Answer: 

Inculcating scientific temper and curiosity among students, increasing understanding levels of students.

Condition: The wavelength of light must be comparable with the size of the slit

Question 2. Aditya participated in a group discussion in his school on “Human eye and its defects” .In the evening he noticed that his father is reading a book by placing it at a distance of 50 cm or more from his eye. He advised him for his eye check-up.

• Suggest the focal length/power of the reading spectacle for him, so that he may easily read the book placed at 25 cm from eye.

• Name the value displayed by Aditya.

Answer:

Determining ‘focal length using lens formula and finding power ‘P’

caring nature, Sympathy

Question 3. Vinod was watching a program on the topic MOON on the Discovery channel. He came to know from the observations recorded from the surface of Moon that the sky appears dark from there. He got surprised and wanted to know the reason behind it. He discussed it with his friends, and they explained the reason behind it.

(a) Name the value that was displayed by Vinod and his friends.

Answer:

Vinod : Curiosity, Scientific temper. Friends: helping nature

(b) State the reason why sky appears dark from the moon.

Answer:

No atmosphere hence no scattering.

Question 4. Ramesh and Arwind were playing near a river. The river appeared shallow to them .Hence they decided to have fun by playing in the river water. Ramesh’s friend Madan happened to pass through. He noticed the intention of the children .Immediately he instructed them not to indulge in adventure and explained them that the river was much deeper than it appeared. This way he avoided a mishappening.

(a) What qualities do Madan displayed.

Answer:

Caring nature, Social responsibility.

(b) With the help of a ray diagram explain why water appeared less deep?

Answer:

Correct diagram showing real depth and apparent depth.

Question 5. Balan was very much fascinated towards astronomy that he decided to make a telescope He carefully studied about the construction of telescope and prepared his own model and presented his ideas in a science seminar and got first prize.

(a) What qualities do Balan posses?

Answer:

Scientific temper, curiosity, in depth understanding of the concept.

(b) What kind of telescope he might have made and draw ray diagram for the same

Answer:

Astronomical telescope, Ray diagram.

Question 6. A teacher has given three lenses 0.5D, 4.0D and 10.0D to a student. He is not sure as to which lens would be used for constructing a good astronomical telescope. So he consulted his seniors and the teacher and construct a telescope. Later he showed the telescope to the junior classes and explained about the choice of lenses.

(a) What value has he shown by doing these?

(b) Which lenses are used as objective and which one is an eye piece?

Answer:

(a) Curiosity, Scientific temper.

(b) Objective-0.5D eyepiece -10D

Question 7. A child is observing a thin film such as a layer of oil on water show beautiful colours when illuminated by white light. He feels happy and surprised to see this. His teacher explains him the reason behind it. The child then gives an example spreading of kerosene oil on water to prevent malaria and dengue.

(a) What value was displayed by his teacher?

(b) Name the phenomenon involved.

Answer:

(a) Curiosity, Scientific temper.

(b) Interference of light.

Question 8. Ramu while doing the experiment for determination of focal length of a convex lens ,suddenly dropped the lens and it got broken into to two halves along its axis .Then Ramu asked the teacher whether even the broken piece will form the image, the teacher answered in the affirmative and showed the image also.

(a) What qualities are exhibited by Ramu?

Answer:

Curiosity, Scientific temper.

(b) What will be the nature of the image formed?

Answer:

Same size, Less intensity.

Question 9. Suman and Arti are friends, both studying in class 12th .Suman is a science student and Arti is a arts student .both of them go to market to purchase sun glasses. Arti feels that any colored glasses with fancy look are good enough. Suman tells her to look for UV protection glasses, Polaroid glasses and photo-sensitive glasses.

Read the following passage and answer the following questions:

(a) What are UV protection glasses, Polaroid glasses and photo sensitive glasses?

(b) What values are displayed by Suman?

Answer:

(a) UV protection glasses are those which filter ultra violet rays they are harmful to our eyes. Polaroid glasses help in reducing the glare. Photo sensitive glasses get darker in strong day light. They protect our eyes from strong sunlight especially at noon.

(b) Suman has displayed concern for her friends. She has put to use the knowledge she acquired in her science. Mugging up things for examination is of no use. What we are taught in the class room must be used in practice.

Question 10. During summer vacation Radha and Rani decided to go for a 3 D FILM. They have heard about this film through their friends. They were asked buy special glasses to view the film. Before they go for a movie, they approached their Physics teacher to know about these glasses. Physics teacher explained when two polarizer’s are kept perpendicular to each other(crossed polarizer’s) the left eye sees only the image from the left end of the projector and the right eye sees only the image from the right lens. The two images have the approximate perspectives that the left and right eyes would see in reality the brain combine the images to produce a realistic 3-D effect.

(a) What qualities do these girls possess?

(b) What do you mean by Polarization?

(c) Mention the other applications of polarization.

Answer:

(a) Curiosity to learn, approaching the teacher to learn new tthings, inquisitiveness

(b) Refer NCERT text book) 

(c) Sun glasses, LCD,CD players.

Value Based Questions

Question 1. Rahul was driving a car and suddenly became aware of a loud sound coming from behind. He looked through his rear-view mirror and saw an ambulance. He recalled reading that such emergency vehicles often have their name written in the mirror writing. He quickly made way for the ambulance, murmuring a quick prayer for the speedy recovery of the patient inside the ambulance.

(i) What type of mirroris as a rear view mirror and why?

(ii) what values did Rahul exhibit ?

Answer:

(i) Convex mirror ,to get a wide view of traffic behind

(ii) Compassion, courtesy, concern for others, knowledgeable

Question 2. Rekha and Preethi were classmates. Preethi was a bright girl and had a quick grasping power. However Rekha noticed that Preethi was not her usual self for the past few days. Rekha found out that Preethi was not able to see the letters on the board properly and also complained of frequent headaches. Rekha suggested to Preethi to get her eye checked .Preethi followed Rekha’s suggestion and thanked her saying she felt very comfortable after wearing the spectacles.

(i) What was the eye defect that Preethi had?

(ii) How can it be corrected?

(iii) Rekha was a true friend. Justify.

Answer:

(i) Myopia

(ii) wearing spectacles made of concave lens

(iii) sympathy ,kind, helpful and caring nature, concern

Question 3. Nitin wanted to buy a gift for his sister and so entered a gift shop. The gift shop had many glass items. On looking closely, he found many of the beverage glasses used for cool drinks had big thick glass walls. He decided not to buy these glasses because he knew that this gives a false impression that there is more amount of liquid inside the glass.

(i) Which physical quantity remains constant when light travels from one medium to another?

(ii) What values can you associate with Nitin decision?

Answer:

(i) Light rays from inside the glass bend away from the normal and appear to diverge

(ii) affection, patience, knowledge about refraction