Question

D. LONG-ANSWER QUESTIONS: Answer in about 30-40 w
1. We depend on light energy for food and fuel. Explain.
2. Describe a simple experiment to show that light travels in stra
3. List three properties of a shadow.
4. Draw a diagram to show the eclipse of the sun. Mark the area
a. total solar eclipse.
b. partial solar
5. In what ways is an image different from a shadow?
6. Draw a diagram to show the formation of the image of a dist
7. Draw a diagram to show reflection of a ray of light by a plan
HOTS QUESTIONS: Think and answer.
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Answer 1

Answer:

diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band?

(b) In what way is diffraction from each slit related to the interference pattern in a double-slit experiment?

(c) When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why?

(d) Two students are separated by a 7 m partition wall in a room 10 m high. If both light and sound waves can bend around obstacles, how is it that the students are unable to see each other even though they can converse easily.

(e) Ray optics is based on the assumption that light travels in a straight line. Diffraction effects (observed when light propagates through small apertures/slits or around small obstacles) disprove this assumption. Yet the ray optics assumption is so commonly used in understanding location and several other properties of images in optical instruments. What is the justification?

Q2

Form the pair of linear equations in the following problems and find their solutions (if they exist) by any algebraic method :

(i) A part of monthly hostel charges is fixed and the remaining depends on the number of days one has taken food in the mess. When a student A takes food for 20 days she has to pay Rs.1000 as hostel charges whereas a student B, who takes food for 26 days, pays Rs.1180 as hostel charges. Find the fixed charges and the cost of food per day.

(ii) A fraction becomes

3

1

when 1 is subtracted from the numerator and it becomes

4

1

when 8 is added to its denominator. Find the fraction.

(iii) Yash scored 40 marks in a test, getting 3 marks for each right answer and losing 1 mark for each wrong answer. Had 4 marks been awarded for each correct answer and 2 marks been deducted for each incorrect answer, then Yash would have scored 50 marks. How many questions were there in the test?

(iv) Places A and B are 100 km apart on a highway. One car starts from A and another from B at the same time. If the cars travel in the same direction at different speeds, they meet in 5 hours. If they travel towards each other, they meet in 1 hour. What are the speeds of the two cars?

(v) The area of a rectangle gets reduced by 9 square units, if its length is reduced by 5 units and breadth is increased by 3 units. If we increase the length by 3 units and the breadth by 2 units, the area increases by 67 square units. Find the dimensions of the rectangle.

Q3

The words given against the sentences below can be used both as nouns and verbs. Use them appropriately to fill in the blanks.

1. (i) The two teams have_________ three matches already. (play)

(ii) The last day's _________ was excellent.

2. (i) She has a lovely _________.(face)

(ii) India __________ a number of problems these days.

3. (i) He made his ____________in eassay-writing. (mark)

(ii) Articles __________ 'sold' are reserved.

4. (i) The police are ___________ the area to catch the burglars. (comb)

(ii) An ordinary plastic _______ costs five rupees.

5. (i) He gave a ____________ in answer to my question. (smile)

(ii) We also ___________ to see him smile.

6. (i) He said he ___________ to be invited to the party. (hope)

(ii) We gave up ___________ of his joinning the party.

7. (i) The boys put up a good athletic ________. (show)

(ii) The soldiers ___________ great courage in saving people from floods.

8. (i) You deserve a ___________ on the back for your good performance. (pat)

(ii) The teacher ____________ the child on the cheek to encourage her.