11. Specification of two electrical heaters are given below
(a) Which heater require a fuse of higher amperage ?
(b) Which of the heaters generate more heat when they work for 5 minutes under the same voltage rating ? Explain the reason.
Answer
a Heater B
b.Heater B . When resistance decreases, current increases, which makes heat to increases.
12. Two rays of light OA and OB are coming from an object 'O', is tailing obliquely on the surface of a plane mirror as shown.
a) Draw a ray diagram indicating the image formation.
b) Write anv two properties of the image formed in this.
Answer
a)
13. A ray of light falling obliquely from air to a glass slab is shown in the figure.
(a) Find out the angle of incidence.
(b) Why the angle of refraction is less than that of the angle of incidence in this case ?
(c) How can you calculate the refractive index of the material of this slab ? (calculation not required)
Answer
a . $$60^{o}(90^{}-30^{o})$$
b. Because the ray of light bend towards the normal, when light travels to denser medium.
c.$$n = \frac{sin i}{sin r} = \frac{sin60}{sin33}$$
14. The picture represents a method of rectification of the defect of an eye using a lens of suitable focal length.
(a) Name the disorder of this eye.
(b) Give two reasons for this defect.
(c) Explain the role of concave lens in the rectification of this defect.
Answer
a. Myopia
b. (i) The Power of eye lens increases.
(ii)The length of the eyeball increases.
c. A concave lens causes the light rays to diverge before they strike the length of the eye so that the image is formed on the retina . It is used to correct Myopia
15.(a) What will be the marking on a cooking gas cylinder that has a maturity period upto March - 2020 ?
(b) Write any two precautions to be taken to avoid accidents due to ' LPG' leakage.
Answer
a) A 2020
b) Examine the rubber tube at regular intervals. Turn on the knob of stove only after the regulator is turned on.
Heater – A
|
Heater - B
|
Resistance - 690 Ω
Working Voltage - 230 V
|
Resistance - 460 Ω
Working Voltage - 230 V
|
(b) Which of the heaters generate more heat when they work for 5 minutes under the same voltage rating ? Explain the reason.
Answer
a Heater B
b.Heater B . When resistance decreases, current increases, which makes heat to increases.
12. Two rays of light OA and OB are coming from an object 'O', is tailing obliquely on the surface of a plane mirror as shown.
a) Draw a ray diagram indicating the image formation.
b) Write anv two properties of the image formed in this.
Answer
a)
b)Virtual erect, Same size
13. A ray of light falling obliquely from air to a glass slab is shown in the figure.
(b) Why the angle of refraction is less than that of the angle of incidence in this case ?
(c) How can you calculate the refractive index of the material of this slab ? (calculation not required)
Answer
a . $$60^{o}(90^{}-30^{o})$$
b. Because the ray of light bend towards the normal, when light travels to denser medium.
c.$$n = \frac{sin i}{sin r} = \frac{sin60}{sin33}$$
14. The picture represents a method of rectification of the defect of an eye using a lens of suitable focal length.
(b) Give two reasons for this defect.
(c) Explain the role of concave lens in the rectification of this defect.
Answer
a. Myopia
b. (i) The Power of eye lens increases.
(ii)The length of the eyeball increases.
c. A concave lens causes the light rays to diverge before they strike the length of the eye so that the image is formed on the retina . It is used to correct Myopia
15.(a) What will be the marking on a cooking gas cylinder that has a maturity period upto March - 2020 ?
(b) Write any two precautions to be taken to avoid accidents due to ' LPG' leakage.
Answer
a) A 2020
b) Examine the rubber tube at regular intervals. Turn on the knob of stove only after the regulator is turned on.
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