TextBook Solutions
- Explain why the planets do not twinkle? Planets are much closer to the earth and are seen as extended sources. So, a planet may be considered as a collection of a large number of p... 1
- Why do stars twinkle? Stars twinkle due to atmospheric refraction of starlight. As the stars are very far away, they behave as almost point sources of light. A so... 1
- What happens to the image distance in the eye when we increase the distance of an object from the eye? The image is formed on the retina even on increasing the distance of an object from the eye. For this eye lens becomes thinner and its focal... 1
- Why is a normal eye not able to see clearly the objects placed closer than 25 cm? A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond... 1
- Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. A person suffering from hypermetropia can see distinct objects clearly but faces difficulty in seeing nearby objects clearly. It happens bec... 1
- The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to https://youtu.be/21zM3lHSEHg 2
- A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision he The power P of a lens of focal length f is given by the relationP= 1/f (i) Power of the lens used for correcting distant vision = - 5.5 D Fo... 1
- 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 Correct option is c) ciliary muscles 2
- The least distance of distinct vision for a young adult with normal vision is about (a) 25 m (b) 2.5 cm (c) 25 Correct option is c) 25 cm 2
- The human eye forms the image of an object at its (a) cornea (b) iris (c) pupil (d) retina Correct option is d) retina 2
- The human eye can focus objects at different distances by adjusting the focal length of the eye lens Correct option is b) accommodation 2
- A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is The student is suffering from myopia or short-sightedness. The defect can be corrected by the use of concave (diverging ) lens of an appropr... 1
- What is the far point and near point of the human eye with normal vision? The near point of the eye is the minimum distance of the object from the eye, which can be seen distinctly without strain. For a normal huma... 1
- A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective A person with a myopic eye should use a concave lens of focal length 1.2 m so as to restore proper vision. 1
- What is meant by power of accommodation of the eye? The ability of the eye lens to adjust its focal length, so as to clearly focus rays coming from distant as well a near objects on the retina... 1
- Explain the following. (a) Why is the tungsten used almost exclusively for filament of electric lamps? a) The melting point and of Tungsten is an alloy which has very high melting point and very high resistivity so does not burn easily at a hi... 2
- An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is Rate of heat produced by a device is given by the expression for power as, P= I²R Where, Resistance of the electric heater, R= 8 Ω Current d... 1
- Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes? Energy consumed by an electrical appliance is given by the expression,H= Pt Where, Power of the appliance = P Time = t Energy consumed by a... 1
- Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. Both the bulbs are connected in parallel. Therefore, potential difference across each of them will be 220 V, because no division of voltage... 1
- Compare the power used in the 2 Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1 Ω and 2 (i) Potential difference, V = 6 V 1 Ω and 2 Ω resistors are connected in series. Therefore, equivalent resistance of the circuit, R = 1 + 2... 1
- 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 https://www.youtube.com/watch?v=Ru4TReFRK7A&ab_channel=Darshanclasses 2
- Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can Resistance R₁ of the bulb is given by the expression, Supply voltage, V = 220 V Maximum allowable current, I = 5 A Rating of an electric bul... 2
- Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of https://youtu.be/LggubtJYvrU 2
- How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line? For x number of resistors of resistance 176 Ω, the equivalent resistance of the resistors connected in parallel is given by Ohm's law asV= I... 1