How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
Infinite number of images will be formed due to multiple reflections of light. The number of images can be determined as;
Describe the construction of a kaleidoscope.
Draw a labeled sketch of the human eye.
Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table (b) Chalk powder
(c) Cardboard surface (d) Marble floor with water spread over it
(e) Mirror (f) Piece of paper
(a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.21).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?
Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.
What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
Explain how you can take care of your eyes.
State the laws of reflection.
Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teachers advise?
Which of the following can be beaten into thin sheets?
(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen
Fill in the blanks
(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.
(b) The passage of an electric current through a solution causes ______________ effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.
(d) The process of depositing a layer ofany desired metal on another material by means of electricity is called .
Give two examples each of situations in which you push or pull to change the state of motion of objects.
Fill in the blanks:
(a) Friction opposes the _____________ between the surfaces in contact with each other.
(b) Friction depends on the _____________ of surfaces. (c) Friction produces __________.
(d) Sprinkling of powder on the carrom board ________ friction.
(e) Sliding friction is ___________ than the static friction.
List conditions under which combustion can take place.
Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has irregular shape. (T/F)
Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.
Fill in the blanks:
(a) A place where animals are protected in their natural habitat is called .
(b) Species found only in a particular area is known as .
(c) Migratory birds fly to far away places because of changes.
What are the different ways in which water gets contaminated ?
Explain the importance of reproduction in organisms.
Arrange the following boxes in proper order to make a flow chart of sugarcane crop production.
Explain the process of formation of petroleum.
When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
Explain circumstances leading to acid rain. How does acid rain affect us?
The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transfered to the thin copper plate. Which electrode should be attached to the positive terminal of battery and why?
Make a labelled diagram of a candle flame.
Explain why the sliding friction is less than the static friction.
An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Explain how deforestation leads to reduced rainfall.
Give two examples each of situations in which you push or pull to change the state of motion of objects.