Silicon is a semiconductor material used to manufacture solar cells because its electronic properties are ideal for converting sunlight into electricity. Carbon, phosphorus, and sulphur do not have the semiconductor properties required for the photovoltaic effect.
Q2mcq1 mark
In an electric circuit to get an equivalent resistance $R_s$ four resistors of 2 $\Omega$ each are first connected in series. Later to get an equivalent resistance of $R_p$ the same resistors are connected in parallel. Then the ratio of $R_s / R_p$ is
a.
16 : 1
Correct Answer
b.
2 : 1
c.
4 : 1
d.
8 : 1
Step-by-Step AI Explanation
Verified Method
For four resistors each of $R = 2 \Omega$ in series, $R_s = R + R + R + R = 4 \times 2 = 8 \Omega$. For the same resistors in parallel, $\frac{1}{R_p} = \frac{1}{2} + \frac{1}{2} + \frac{1}{2} + \frac{1}{2} = \frac{4}{2} = 2$, so $R_p = 0.5 \Omega$. The ratio $R_s / R_p = 8 / 0.5 = 16$. Thus, the ratio is 16:1.
Q3mcq1 mark
Right statement regarding the colour of the scattered sunlight and the size of scattering atmospheric particles is
a.
small particles scatter red colour
b.
big particles scatter blue colour
c.
big particles scatter violet colour
d.
too larger particles scatter all colours equally
Correct Answer
Step-by-Step AI Explanation
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According to Rayleigh scattering, smaller particles scatter shorter wavelengths (blue/violet), whereas larger particles (like water droplets in clouds) scatter all wavelengths almost equally, which is why clouds appear white. Choice (a), (b), and (c) are incorrect because they misidentify the relationship between particle size and wavelength scattering.
Q4short answer1 mark
Write the symbols of the following components used in an electric circuit :
i) Combination of two cells
ii) Wires crossing without joining.
Step-by-Step AI Explanation
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i) Combination of two cells: Two long lines (positive terminals) and two short lines (negative terminals) connected by lines, represented as $| | | |$.
ii) Wires crossing without joining: Two lines crossing each other with a small 'hump' or loop on one of the lines to indicate they are not touching.
Q5short answer1 mark
Can an electric heater of 2kW be connected to a domestic circuit rated 15 A and has a potential difference of 220V ? Support your answer.
Step-by-Step AI Explanation
Verified Method
The power $P = 2kW = 2000W$. The voltage $V = 220V$. The current drawn by the heater is $I = P/V = 2000/220 \approx 9.09A$. Since the current drawn (9.09 A) is less than the rated capacity of the circuit (15 A), the electric heater can be safely connected.
Q6short answer2 marks
What is spectrum of white light ? Name any two phenomena that occur in the atmosphere due to the refraction of light.
Step-by-Step AI Explanation
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The spectrum of white light is the band of seven colours (VIBGYOR) obtained when white light is dispersed by a prism. Two atmospheric phenomena caused by the refraction of light are:
1. Twinkling of stars.
2. Advanced sunrise and delayed sunset.
Q6short answer2 marks
What is cataract of eye ? What are the near point and far point of the human eye with normal vision ?
Step-by-Step AI Explanation
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Cataract is a condition in which the crystalline lens of the human eye becomes milky and cloudy due to the formation of an opaque membrane, leading to a partial or complete loss of vision. For a normal human eye, the near point is $25 cm$ and the far point is at infinity.
Q7short answer2 marks
“Production of nuclear energy is advantageous and also disadvantageous.” Clarify this statement with suitable explanation.
Step-by-Step AI Explanation
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Advantages: Nuclear energy is advantageous because a very small amount of fuel produces a huge amount of energy, and it does not emit greenhouse gases like carbon dioxide during operation.
Disadvantages: It is disadvantageous due to the risks of improper nuclear waste storage (radioactive pollution), the high cost of installation, and the risk of accidental leakage of harmful radiation.
Q8short answer2 marks
A person who has a defect of the eye as shown in the below figure purchases a spectacle having lens of – 2·0D power. Is this lens suitable to rectify the eye defect of that person ? Analyse.
Step-by-Step AI Explanation
Verified Method
The figure shows that the rays from a near object are focusing behind the retina, which is characteristic of hypermetropia (farsightedness). Hypermetropia is corrected using a convex lens, which has a positive power. Since the person purchased a lens with a negative power ($-2.0 D$), which is a concave lens, it is not suitable to rectify this specific defect.
Q9long answer3 marks
Draw the ray diagram of image formation when the object is kept at $2F_1$ of the convex lens. With the help of ray diagram mention the position and the nature of the image formed. ($F_1$ : Principal focus of the lens)
Step-by-Step AI Explanation
Verified Method
Ray Diagram Description: An object is placed at $2F_1$ in front of a convex lens. A ray parallel to the principal axis passes through the focus $F_2$ on the other side. A second ray passing through the optical center $O$ goes straight without deviation. The rays intersect at $2F_2$ on the other side of the lens.
Position of image: At $2F_2$.
Nature of image: Real, inverted, and of the same size as the object.
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$200J$ of heat is produced each second in a $8 \Omega$ resistance. Find the potential difference across the resistor. OR An electric refrigerator rated $300W$ operates 6 hours in a day. What is the cost of the energy to operate it for 30 days at Rs. $7.00$ per kWh?
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A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is
i) pushed into the coil ?
ii) withdrawn from inside the coil ?
iii) held stationary inside the coil ?
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In domestic circuits, i) What are the reasons for overloading? ii) Explain the working of earth wire. OR A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is i) pushed into the coil? ii) withdrawn from inside the coil? iii) held stationary inside the coil?
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a) State the right hand thumb rule. Write any two properties of the magnetic field lines.
b) What is solenoid ? How can this be converted into an electromagnet ?
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Observe the electronic configurations of four elements given in the following table and answer the below given question: Elements: e (2, 8, 2), f (2, 7), g (2, 8, 8, 1), h (2, 8, 7). Arrange these elements in the decreasing order of their atomic radii (atomic size).
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Simultaneously red and blue litmus papers are dipped in the brine solution and in the aqueous product produced by subjecting that solution to electrolysis. What changes do you observe in litmus papers? Support your answer with reasons. OR Observe the pH values of four solutions given in the following table and answer the questions below. Solutions: P (10.0), Q (13.7), R (7.0), S (1.2). i) Which solution can be used to prepare an antacid? Why? ii) Which two solutions can be used to get a neutral salt? Why?
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a) Identify the substances that are oxidised and reduced in the following chemical reaction: $ZnO + C \rightarrow Zn + CO$. b) What is rancidity? Mention any two methods to prevent rancidity.
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Given below an incomplete equation that represents a chemical process of converting an unsaturated carbon compound to saturated carbon compound.
i) Complete the equation.
ii) Name the gas ‘x’ and the substance ‘y’ .
iii) What happens if the end products of this reaction react with chlorine in the presence of sunlight ?
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a) Carbon could not form $C^{+4}$ or $C^{-4}$ ions. Why? b) Write the electron dot structure of methane. OR a) How micelles are formed during cleansing action of soap? b) Which are the salts responsible for hardness of water? Detergents are effective even in hard water. Why?
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a) How silver and copper articles lose their shining surface? How does galvanisation protect iron articles? b) Aluminium oxide is an amphoteric oxide. Why?
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Pea plants with round seeds ( RR ) are crossed with pea plants with wrinkled seeds ( rr ). The percentage of plants that are having RR genetic make-up in $F_2$ generation is,
a.
25%
b.
50%
c.
30%
d.
75%
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Given below an incomplete equation that represents a chemical process of converting an unsaturated carbon compound to saturated carbon compound. i) Complete the equation.
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Schematic representation of blood circulation in the mammals is given below :
i) Name the blood vessels ‘x’ and ‘y’.
ii) Which blood vessel has valves ?
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a) Measures of recharging underground water are better than the storage of water on the surface levels of the ground. How ? Explain.
b) Reuse is better than recycling. Why ?
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a) “In human reproduction, the placenta performs a significant role in the development of a foetus into a child.” Justify this statement.
b) How can DNA copying be decided as one of the ways of reproduction in lower organisms ?
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What product is formed in the first step that takes place in the cytoplasm during the respiration in animals ? Write any two differences between aerobic and anaerobic respiration.
OR
a) In what form are the waste products stored in old xylems of plants ?
b) How do the products of photosynthesis transport to all parts of the plant ?
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a) Which part of the human brain controls the following activities ?
i) Involuntary activities
ii) Thinking process
iii) Posture and balance of the body.
b) What are phytohormones ? Name three phytohormones that promote growth.
OR
a) Name the hormones that control the following activities in man :
i) Regulating sugar level in the blood
ii) Regulating the menstrual cycle
iii) Preparing the body to face situation
iv) Regulating the metabolism.
b) Name any two tropisms that occur in plants. Give an example for each.
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a) Human hands and wings of the bird help to trace the evolutionary relationships. How ? Explain the methods of dating of fossils.
b) Changes in the non-reproductive tissues will not inherit. Why ?
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