Find the focal length of a convex mirror whose radius of curvature is 6 cm.
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The relationship between focal length ($f$) and radius of curvature ($R$) for a spherical mirror is $f = \frac{R}{2}$. Given $R = 6$ cm, $f = \frac{6}{2} = 3$ cm. Therefore, the focal length of the convex mirror is 3 cm.
Q3short answer
Find the power of convex lens of focal length 0.2 m.
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The power ($P$) of a lens is defined as the reciprocal of its focal length ($f$) in meters: $P = \frac{1}{f(\text{in meters})}$. Given $f = 0.2$ m, $P = \frac{1}{0.2} = 5$ D. The power of the convex lens is +5 Dioptre.
Q8short answer2 marks
How does the eye accommodate to see far and near objects ?
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Accommodation is the ability of the eye lens to adjust its focal length. The ciliary muscles control the curvature of the lens. To see distant objects, ciliary muscles relax, the lens becomes thin, and focal length increases. To see nearby objects, ciliary muscles contract, the lens becomes thicker (curved), and focal length decreases.
Q9short answer3 marks
A concave lens has focal length of 30 cm. At what distance should the object from the lens be placed so that it forms an image at 20 cm from the lens ?
Step-by-Step AI Explanation
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Given: Focal length of concave lens $f = -30$ cm (concave lens focal length is negative). Image distance $v = -20$ cm (concave lens always forms a virtual image on the same side). Using the lens formula: $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$. Substituting the values: $\frac{1}{-20} - \frac{1}{u} = \frac{1}{-30}$. Rearranging: $-\frac{1}{u} = \frac{1}{20} - \frac{1}{30}$. Taking LCM ($60$): $-\frac{1}{u} = \frac{3-2}{60} = \frac{1}{60}$. Thus, $u = -60$ cm. The object should be placed at a distance of 60 cm from the lens.
Q9short answer2 marks
Why do stars twinkle ? Explain.
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Stars twinkle due to atmospheric refraction. Light from the stars enters the Earth's atmosphere and undergoes continuous refraction through various layers of air with varying optical densities (due to temperature and pressure differences). This causes the apparent position of the star to shift slightly and its intensity to fluctuate, which we perceive as twinkling.
Q10long answer3 marks
Draw the ray diagram for the image formation in a convex lens when the object is placed between $2F_1$ and $F_1$. Mention the position and nature of the image formed. [$F_1$ : Principal focus of the lens]
Step-by-Step AI Explanation
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Ray Diagram Description: Draw a convex lens with an optical center $O$. Place the object $AB$ between $F_1$ and $2F_1$. One ray passes parallel to the principal axis and passes through $F_2$ on the other side. A second ray passes through the optical center $O$ without deviation. They intersect beyond $2F_2$.
Position of image: Beyond $2F_2$.
Nature of image: Real, inverted, and magnified.
Q11short answer3 marks
What are the characteristics of a good source of energy ? Write any two uses of solar cells.
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Characteristics of a good source of energy:
1. It should be easily accessible.
2. It should be easy to store and transport.
3. It should be economical and provide a large amount of work per unit mass.
Uses of solar cells:
1. Used in traffic signals and street lighting.
2. Used to power artificial satellites and space probes.
Q11short answer3 marks
What are the advantages and disadvantages of nuclear energy ?
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Advantages:
1. It produces a large amount of energy from a small quantity of fuel.
2. It does not produce greenhouse gases like carbon dioxide during operation.
Disadvantages:
1. High cost of installation and complex technology.
2. Risk of environmental contamination due to improper storage and disposal of radioactive nuclear waste.
Q12short answer2 marks
Explain Faraday’s experiment related to the electromagnetic induction.
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Michael Faraday connected a coil of wire to a galvanometer. When a bar magnet was moved towards or away from the coil, the galvanometer needle showed a deflection. This indicated that a changing magnetic field induces an electric current in the coil. This phenomenon is known as electromagnetic induction.
Q14mcq1 mark
In the electrolysis of water the gases that are released at cathode and anode and their ratio respectively are,
a.
Hydrogen : Oxygen ; 1 : 2
b.
Oxygen : Hydrogen ; 2 : 1
c.
Hydrogen : Oxygen ; 2 : 1
Correct Answer
d.
Oxygen : Hydrogen ; 1 : 2
Step-by-Step AI Explanation
Verified Method
In the electrolysis of water ($2H_2O \rightarrow 2H_2 + O_2$), hydrogen is produced at the cathode and oxygen at the anode. The stoichiometry of the reaction shows that for every 2 moles of hydrogen, 1 mole of oxygen is produced, resulting in a 2:1 ratio.
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The molecular formula of the fourth member of a homologous series is $C_5H_{10}$. Then, determine and write the molecular formulae of first two members of the same series.
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250 ml of water is taken in each of beaker ‘A’ and beaker ‘B’. About 5 gm of sodium metal is added to the beaker ‘A’ and about 5 gm of calcium metal is added to beaker ‘B’. What are the reasons for the observations that have been noticed here ?
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An iron nail is immersed in copper sulphate solution. Then what type of chemical reaction happens here ? Write the balanced chemical equation for this reaction.
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Draw the diagram of the arrangement of apparatus showing the reaction of zinc granules with dilute sulphuric acid and testing of hydrogen gas by burning and label the hydrogen gas bubbles.
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Solutions ‘A’, ‘B’, ‘C’ and ‘D’ are having pH values of 2, 6, 8 and 13 respectively. Which solution has more $H^+$ and which solution has more $OH^-$ ion concentration ? Why ?
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Solutions ‘A’, ‘B’, ‘C’ and ‘D’ are having pH values of 2, 6, 8 and 13 respectively. Which solutions can be made to react each other to get neutral salts ?
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Observe the given part of periodic table and answer the following questions: Elements a, b, c, d, e with Atomic Number 3, 4, 10, 11, 18. Which elements have + 1 valency ?
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Observe the given part of periodic table and answer the following questions: Elements a, b, c, d, e with Atomic Number 3, 4, 10, 11, 18. Mention the place of element ‘b’ in the modern periodic table.
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a) According to Mendel what are dominant traits and recessive traits ?
b) What is dihybrid cross ? What is the ratio of plant types obtained in the $F_2$ generation of Mendel’s dihybrid experiment ?
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