Why does the Sun appear reddish early in the morning?
In the early morning sun is at the farthest distance from the earth.
When the white light beam passed through the transparent glass tank having clear water, a converging lens is placed between them. After the glass tank a cardboard is placed having a circular hole in it, in which light ray passed on the screen by using another converging lens. Add 200g of sodium thiosulphate and 1- 2ml of concentrated sulphuric acid to 2L of clean water in the tank, then the sulphur particles begins to form in 2- 3 minutes. We can observe the light with the smaller wavelength, i.e, blue from the three sides of the glass tank will scatter and from the fourth side we will see the red light that pass into the circular hole, reaches to the human eyes.
As in the above paragraph mentioned, the sun colour appearance is described in the same way. The sun appears red in the early morning because when the light from the sun near the horizon passes through the atmospheric thick layers, blue light with shorter wavelength will scatter and the red light will reach to the eyes having longer wavelength.
What is the far point and near point of the human eye with normal vision?
Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
Why do stars twinkle?
Explain why the planets do not twinkle.
What is meant by power of accommodation of the eye?
The human eye forms the image of an object at its
(a) cornea. (b) iris. (c) pupil. (d) retina.
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
The least distance of distinct vision for a young adult with normal vision is about
(a) 25 m. (b) 2.5 cm. (c) 25 cm. (d) 2.5 m.
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
The change in focal length of an eye lens is caused by the action of the
(a) pupil. (b) retina.
(c) ciliary muscles. (d) iris.
Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
What is a good source of energy?
Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
What changes can you make in your habits to become more environment-friendly?
What is the difference between a reflex action and walking?
What is the importance of DNA copying in reproduction?
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Why should a magnesium ribbon be cleared before burning in air?
Define the principal focus of a concave mirror.
State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
What is the function of digestive enzymes?
How is food transported in plants?
You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal.
What effect does the concentration of H+(aq) ions have on the nature of the solution?
How does chemical coordination occur in plants?
How would you distinguish experimentally between an alcohol and a carboxylic acid?
The xylem in plants are responsible for
(a) transport of water. (c) transport of amino acids.
(b) transport of food. (d) transport of oxygen.