What is meant by power of accommodation of the eye?
Accommodation is a reflex mechanism in by which eyes changes the focal power to make the farthest and the nearest object clearly visible on the retina. Human beings have the good power of accommodation. Accommodation requires the refraction of light rays when they passed from one medium to another for getting focus on retina. Refraction occurs at the lens and it depends on the angle of the light or distance of the object from cornea. Thus, the degree of refraction is changed by changing the convexity of the lens. And, all of this mechanism is done with the help of ciliary muscles or suspensory ligament also known as accommodation apparatus.
When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
Outline a project which aims to find the dominant coat colour in dogs.
Draw the structure for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal.
*Are structural isomers possible for bromopentane?
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
How is the sex of the child determined in human beings?
(a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Calculate the number of electrons constituting one coulomb of charge.
What is an homologous series? Explain with an example.
Why is variation beneficial to the species but not necessarily for the individual?
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
Name the substance which on treatment with chlorine yields bleaching powder.
What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?
Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
What are the disadvantages of fossil fuels?
What precaution should be taken to avoid the overloading of domestic electric circuits?
Calculate the number of electrons constituting one coulomb of charge.
Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Why does an aqueous solution of an acid conduct electricity?
What effect does the concentration of H+(aq) ions have on the nature of the solution?