Part A
Section-I: 3 x 2 = 6 Marks
Instructions: Write the answers in 2 to 3 sentences. Each question carries 2 marks.
1. Draw the ray diagram when a candle is kept between the pole and focus in front of the concave mirror.
Answer:In this case, the image formed by a concave mirror when the object (candle) is placed between the pole (P) and the focus (F) is virtual, erect, and magnified.
- The ray diagram will show:
- A ray parallel to the principal axis reflects and passes through the focus (F).
- A ray passing through the focus (F) reflects and becomes parallel to the principal axis.
- A ray passing through the center of curvature (C) reflects back on itself.
- The image is formed on the same side as the object.
2. How can you prevent corrosion in metals in our daily life?
Answer:
Corrosion of metals can be prevented by:
- Coating the metal: Applying a protective layer of paint, oil, or plastic to prevent exposure to air and moisture.
- Galvanization: Coating iron or steel with a layer of zinc to protect it from rusting.
- Using alloys: Materials like stainless steel, which are more resistant to corrosion, can replace iron or steel in some applications.
- Cathodic protection: Connecting the metal to a more easily corroded metal (like zinc) to protect it from corrosion.
3. What will happen if we use a thick copper wire in an electric fuse in our houses?
Answer:
If a thick copper wire is used in an electric fuse, the fuse will not blow or melt properly in the event of an overload or short circuit.
- This is because a thick copper wire has a low resistance and can carry more current without heating up, preventing the fuse from breaking the circuit during high current flow.
- A fuse needs a thin wire with higher resistance to heat up and melt when the current exceeds the safe limit.
Section-II: 3 x 4 = 12 Marks
Instructions: Write the answers in 4 to 5 sentences. Each question carries 4 marks.
A) What are the object positions when images are forming as inverted on a screen?
Answer:
For an image to form as inverted on the screen, the object must be placed outside the focus (beyond the focal point) of a concave mirror. The following positions are possible:
- At a distance greater than 2F: The image formed is real, inverted, and smaller than the object.
- At 2F: The image formed is real, inverted, and of the same size as the object.
- Between F and 2F: The image formed is real, inverted, and magnified.
B) What are the object positions of images formed between F2, C2, and at C2 only?
Answer:
For a concave mirror:
- When the object is placed between F2 and C2 (the center of curvature), the image formed is real, inverted, and magnified.
- When the object is placed at C2 (the center of curvature), the image formed is real, inverted, and of the same size as the object.
- In both cases, the image is formed beyond the mirror at a location that is proportional to the object’s distance.
C) What are the image properties when objects are kept at F1 and between F1 and P?
Answer:
- When the object is placed at F1 (focus) of a concave mirror, the image formed is real, inverted, and highly magnified (at infinity).
- When the object is between F1 and P (pole), the image formed is virtual, erect, and magnified. This image will appear behind the mirror and cannot be captured on a screen.
D) What type of lens should we use for all the above cases?
Answer:
For the cases described above, we are dealing with concave mirrors (a type of reflecting surface). However, in the case of lenses:
- A concave lens (diverging lens) is used for forming virtual and erect images.
- Convex lenses (converging lenses) are typically used for focusing light and forming real and inverted images.
- For the given properties, a concave mirror or concave lens (depending on the situation) would be used.
5. Write the working process of the electric motor?
Answer:
An electric motor works on the principle of electromagnetic induction, which states that when a current-carrying conductor is placed in a magnetic field, it experiences a force.
- The motor has a coil of wire placed in a magnetic field.
- When current flows through the coil, it experiences a force due to the magnetic field, which causes the coil to rotate.
- The commutator reverses the direction of current in the coil to keep the rotation continuous.
- As the coil rotates, it converts electrical energy into mechanical energy, powering devices.
6. What are the factors affecting resistance?
Answer:
The resistance (R) of a conductor is affected by the following factors:
- Material of the conductor: Different materials have different resistivities. For example, copper has low resistance, while rubber has high resistance.
- Length of the conductor: Resistance is directly proportional to the length of the conductor. The longer the wire, the higher the resistance.
- Cross-sectional area: Resistance is inversely proportional to the cross-sectional area of the conductor. A thicker wire has less resistance.
- Temperature: The resistance of most materials increases with an increase in temperature. For metals, as the temperature increases, resistance increases due to increased collisions of electrons.
Section-III: 2 x 6 = 12 Marks
Instructions: Write the answers for only 2 questions out of 3 questions. Each answer should be written in 8 to 10 sentences.
7. What is the difference between a concave mirror and a convex mirror?
Answer:
- Concave Mirror:
- The reflecting surface is curved inward.
- It converges light rays to a point, called the focus.
- It can form both real and virtual images depending on the object’s position.
- The image is inverted when the object is beyond the focal point and erect when it is within the focal point.
- It is used in applications like magnifying mirrors, flashlights, and telescopes.
- Convex Mirror:
- The reflecting surface is curved outward.
- It diverges light rays, and the image formed is always virtual, erect, and diminished.
- The image appears to be located behind the mirror.
- It is used in applications like rearview mirrors and security mirrors due to its wide field of view.
8. Write the experiment to show why an electric bulb does not glow in the solutions of glucose and alcohol?
Answer:
To demonstrate that an electric bulb does not glow in solutions of glucose and alcohol, we can perform the following experiment:
- Apparatus: A bulb, battery, connecting wires, and beakers of glucose and alcohol solutions.
- Procedure:
- Prepare two beakers: one with glucose solution and the other with alcohol solution.
- Connect the bulb to a battery in a simple circuit with wires.
- Now, immerse the electrodes of the circuit in the glucose solution and observe the bulb. The bulb will not glow because glucose does not conduct electricity.
- Repeat the process with the alcohol solution, and again, the bulb will not glow.
- Conclusion: Glucose and alcohol are non-electrolytes because they do not dissociate into ions in water, making the solutions non-conductive. Hence, the bulb does not glow.
9. Draw the diagrams for H₂O, NH₃, and BH₃ according to Valence Bond Theory and hybridization?
Answer:
- H₂O (Water):
- Hybridization: sp³
- The oxygen atom forms two sigma bonds with two hydrogen atoms and has two lone pairs of electrons.
- The bond angle is approximately 104.5°.
- NH₃ (Ammonia):
- Hybridization: sp³
- Nitrogen forms three sigma bonds with three hydrogen atoms and has one lone pair of electrons.
- The bond angle is around 107°.
- BH₃ (Borane):
- Hybridization: sp²
- Boron forms three sigma bonds with three hydrogen atoms and has an empty p-orbital, making it electron-deficient.
- The bond angle is 120°.
Part B: Multiple Choice Questions (1 x 10 = 10 Marks)
Instructions: Write the answers for all multiple choice questions. Each question carries 1 mark.
Any correction will be invalid.
1. Hydrophobic ends of soap particles are attracted to ______.
( )
a) Mud or Grease
b) Water
c) Soap
d) Hydrophilic
Answer: a) Mud or Grease
Explanation: The hydrophobic ends of soap molecules are non-polar and are attracted to grease or oil, which is also non-polar. These ends help to dissolve or break down grease and oil. The hydrophilic (water-attracting) ends, on the other hand, interact with water.
2. What is the carbon compound used in cough syrup?
( )
a) Ketone
b) Ether
c) Ester
d) Ethanol
Answer: d) Ethanol
Explanation: Ethanol is often used in cough syrup as a solvent. It also has mild antiseptic properties and helps dissolve active ingredients in the syrup, making it effective for medicinal purposes.
3. How many times stronger is Graphene compared to steel?
( )
a) 200
b) 250
c) 300
d) 150
Answer: b) 250
Explanation: Graphene is approximately 250 times stronger than steel. It is known for its remarkable strength-to-weight ratio, and this quality makes it a promising material for various advanced applications, including electronics and construction.
4. Mercury is taken from ______ ore.
( )
a) Gypsum
b) Galena
c) Haematite
d) Cinnabar
Answer: d) Cinnabar
Explanation: Cinnabar is the primary ore from which mercury (also known as quicksilver) is extracted. Cinnabar is a mercury sulfide mineral (HgS), and it has been used for centuries to obtain mercury.
5. What is the resultant resistance when bulbs are connected in series as 2Ω, 4Ω, and 6Ω?
( )
a) 12Ω
b) 10Ω
c) 14Ω
d) 8Ω
Answer: a) 12Ω
Explanation: When resistors are connected in series, the total resistance is the sum of the individual resistances.
So, Rtotal=2Ω+4Ω+6Ω=12ΩR_{total} = 2Ω + 4Ω + 6Ω = 12ΩRtotal=2Ω+4Ω+6Ω=12Ω.
6. Which element has the greatest ionization energy?
( )
a) Li
b) Na
c) K
d) Fr
Answer: a) Li
Explanation: Lithium (Li) has the highest ionization energy among the options. Ionization energy increases across a period and decreases down a group in the periodic table. Lithium, being the first element in the alkali metal group, has the smallest atomic size and the highest ionization energy.
7. What is the velocity of light (c) in space?
( )
a) 3 x 10⁹ m/s
b) 3 x 10⁸ m/s
c) 3 x 10¹⁰ m/s
d) 10⁷ m/s
Answer: b) 3 x 10⁸ m/s
Explanation: The speed of light in a vacuum is approximately 3 x 10⁸ meters per second (m/s). This is a fundamental constant in physics, denoted by c, and it is crucial in equations like Einstein’s theory of relativity.
8. The stinging hair of leaves of the nettle plant injects ______ into our body.
( )
a) Hydrochloric acid
b) Methanoic acid
c) Sulphuric acid
d) Formic acid
Answer: d) Formic acid
Explanation: The stinging hairs of the nettle plant inject formic acid into the skin, causing a stinging or burning sensation. Formic acid is also found in the venom of ants.
9. ________ is used for melanoma cancer treatment.
( )
a) Graphite
b) Diamond
c) Graphene
d) Fullerene
Answer: c) Graphene
Explanation: Graphene has shown promise in the treatment of various cancers, including melanoma. Researchers are investigating graphene’s potential as a drug delivery system and its ability to target cancer cells more effectively than traditional therapies.
10. Alloy of Fe, Ni, Cr is ________.
( )
a) Bronze
b) Stainless Steel
c) Brass
d) Sn
Answer: b) Stainless Steel
Explanation: Stainless steel is an alloy of iron (Fe), nickel (Ni), and chromium (Cr). It is known for its resistance to rust and corrosion, making it widely used in kitchenware, surgical instruments, and construction materials.