PART – A
Section-I: Marks: 6 (3 x 2 = 6 marks)
1. Why don’t you preserve pickles, sour substances in brass and copper vessels?
Answer:
Pickles and sour substances should not be stored in brass or copper vessels because both these metals react with acids present in the pickle. This reaction results in the formation of harmful compounds, such as salts of copper or brass, which can be toxic when consumed. Additionally, the acidic nature of the pickles can cause the metal to corrode, leading to contamination of the food.
2. When we use a plane mirror in a rearview mirror in vehicles, what are the properties of the image formed?
Answer:
The image formed by a plane mirror in a rearview mirror is virtual, erect, and of the same size as the object. The image is laterally inverted (left appears right and right appears left), and it is formed behind the mirror. The distance of the image from the mirror is equal to the distance of the object in front of the mirror, providing a clear reflection of objects behind the vehicle.
3. What will happen when we use a convex mirror in a solar cooker?
Answer:
Convex mirrors diverge light rays, which means they spread the light outwards. This makes them unsuitable for use in solar cookers, which require concentrated light. In a solar cooker, a concave mirror is typically used to focus sunlight onto a specific area to generate high heat. A convex mirror would scatter the light, reducing the effectiveness of the solar cooker.
Section-II: Marks: 12 (3 x 4 = 12 marks)
4. What is the importance of pH in our daily life?
Answer:
pH plays a vital role in our daily life because it affects various biological and chemical processes. For instance:
- In our digestive system, the stomach maintains an acidic pH (around 2) to aid digestion.
- pH affects the quality of water; water with a neutral pH is ideal for drinking.
- In agriculture, the pH of the soil determines nutrient availability for plants.
- Personal care products like shampoos, soaps, and deodorants are formulated to match the skin’s natural pH for better results and skin health.
5. Write the applications of total internal reflection.
Answer:
Total internal reflection has several practical applications:
- Optical fibers: It is used in communication networks where light signals are transmitted through fiber optic cables.
- Prisms in binoculars: Prisms in optical instruments like binoculars and periscopes use total internal reflection to direct light.
- Mirages: Natural phenomena like mirages are a result of total internal reflection of light in the atmosphere.
- Endoscopes: Medical endoscopes use optical fibers to transmit light and images for internal examination.
6. How can you correct the myopia defect, explain with the help of a picture?
Answer:
Myopia (nearsightedness) is a vision defect where distant objects appear blurry while close objects can be seen clearly. This happens when the eye is too long, or the cornea has too much curvature, causing light to focus in front of the retina.
To correct myopia, concave lenses (diverging lenses) are used. These lenses help diverge the incoming light rays, so they focus properly on the retina instead of in front of it. The picture would show the eye with a concave lens and the light rays properly focusing on the retina.
Section-III: Marks: 12 (2 x 6 = 12 marks)
7. Ionization energy of an element depends on what factors?
Answer:
Ionization energy is the energy required to remove an electron from an atom in its gaseous state. It depends on the following factors:
- Atomic size: Smaller atoms have higher ionization energy because the electrons are closer to the nucleus and more strongly attracted.
- Nuclear charge: A higher positive charge in the nucleus (more protons) increases ionization energy as the attraction between the nucleus and electrons is stronger.
- Electron shielding: Electrons in inner shells shield outer electrons from the full force of the nuclear charge. The more shielding, the lower the ionization energy.
- Electron configuration: Atoms with a stable electron configuration (e.g., noble gases) have higher ionization energies because they do not easily lose electrons.
8. Show that the ratio of V/I is a constant for a conductor.
Answer:
The ratio of voltage (V) to current (I) is known as resistance (R). According to Ohm’s law:V=I×RV = I \times RV=I×R
This implies:VI=R\frac{V}{I} = RIV=R
For an ideal conductor, resistance (R) is constant. Therefore, the ratio of voltage to current (V/I) remains constant for a conductor, irrespective of the values of V or I, as long as the temperature and material of the conductor do not change.
9. How do soap particles remove greasy or mud particles from cloth?
Answer:
Soap molecules have hydrophobic (water-repelling) and hydrophilic (water-attracting) ends. When soap is applied to greasy or muddy surfaces, the hydrophobic tail of the soap molecule attaches to the grease or dirt, while the hydrophilic head interacts with water. The soap molecules form tiny clusters called micelles, where the grease or dirt is trapped inside. When washed with water, the hydrophilic heads of soap molecules allow the entire micelle to be rinsed away, thus cleaning the cloth.
Part-B: Multiple Choice Questions (1 x 10 = 10 marks)
1. In the hydrogenation reaction of oil, ________ element is used as a catalyst.
A) Nickel
B) Hydrogen
C) Oxygen
D) Copper
Answer: A) Nickel
Explanation: In the hydrogenation process, hydrogen is added to unsaturated oils, and nickel is commonly used as a catalyst to speed up the reaction.
2. ________ flux is used when we get iron from Haematite ore.
A) Si
B) Fe
C) Cao
D) Sn
Answer: C) Cao (Calcium oxide)
Explanation: Calcium oxide (CaO) is used as a flux in the extraction of iron from Haematite ore (Fe2O3) in a blast furnace. It combines with impurities like silica to form slag.
3. Which one of the following elements has less reactivity?
A) Zn (Zinc)
B) Na (Sodium)
C) Ca (Calcium)
D) Au (Gold)
Answer: D) Au (Gold)
Explanation: Gold (Au) is a noble metal and is highly resistant to corrosion and oxidation. This means it has very low reactivity compared to metals like sodium (Na) and calcium (Ca).
4. What are the units of magnetic flux density?
A) Ampere
B) Volts
C) Tesla
D) Decibel
Answer: C) Tesla
Explanation: Magnetic flux density is measured in Tesla (T), which is the unit of magnetic field strength in the International System of Units (SI).
5. Magnitude of electric charge eee = ________.
A) 1.602 x 10−19^{-19}−19 C
B) 1.602 x 1019^1919 C
C) 1.206 x 10−19^{-19}−19 C
D) 1.206 C
Answer: A) 1.602 x 10−19^{-19}−19 C
Explanation: The magnitude of the elementary charge (e), which is the charge of a proton, is 1.602 x 10−19^{-19}−19 C.
6. What is the bond angle of water?
A) 90°
B) 120°
C) 180°
D) 104°
Answer: D) 104°
Explanation: The bond angle in a water molecule (H₂O) is approximately 104° due to the repulsion between the lone pairs of electrons on the oxygen atom.
7. Which element has less electronegativity?
A) F (Fluorine)
B) Cs (Cesium)
C) O (Oxygen)
D) Fe (Iron)
Answer: B) Cs (Cesium)
Explanation: Cesium (Cs) has the least electronegativity among the options because electronegativity decreases as you move down the periodic table. Fluorine (F) is the most electronegative element.
8. What is the period number of Actinides?
A) 6th period
B) 5th period
C) 4th period
D) 7th period
Answer: A) 6th period
Explanation: The actinide series corresponds to the 6th period of the periodic table. These elements include actinium, thorium, uranium, and others.
9. ________ principle is used to identify the maximum electrons in a subshell.
A) 2(2l + 1)
B) 2n2^22
C) 0 to n-1
D) n + l
Answer: B) 2n2^22
Explanation: The maximum number of electrons in a shell is given by the formula 2n2^22, where n is the principal quantum number. This formula applies to the maximum number of electrons in any given shell.
10. What is the distance between the retina and the eye lens of a healthy man?
A) 2.27 cm
B) 1.7 cm
C) 2.5 cm
D) 30 cm
Answer: A) 2.27 cm
Explanation: In a healthy human eye, the distance between the eye lens and the retina is approximately 2.27 cm. This distance can vary slightly among individuals but is generally around this value for normal vision.