The power of a lens is + 2D. Then the focal length of that lens is
a.
0.5 m
Correct Answer
b.
2 m
c.
0.2 m
d.
5 m
Step-by-Step AI Explanation
Verified Method
The formula for power ($P$) is $P = \frac{1}{f}$ where $f$ is in meters. Given $P = +2D$, we have $2 = \frac{1}{f}$, which means $f = \frac{1}{2} = 0.5\text{ m}$. Thus, (a) is correct.
Q2mcq1 mark
The resistivities of some materials at 20°C are given in the table below:
Materials | Resistivity ($\Omega m$)
K | $2.63 \times 10^{-8}$
L | $5.20 \times 10^{-8}$
M | $1.60 \times 10^{-8}$
N | $6.84 \times 10^{-8}$
The best conductor of electricity among these materials is
a.
N
b.
K
c.
M
Correct Answer
d.
L
Step-by-Step AI Explanation
Verified Method
The best conductor is the material with the lowest electrical resistivity. Comparing the values: $1.60 \times 10^{-8} < 2.63 \times 10^{-8} < 5.20 \times 10^{-8} < 6.84 \times 10^{-8}$. Material M has the lowest resistivity, so it is the best conductor.
Q3short answer1 mark
Write the symbol diagram of the following components used in the electric circuit:
i) Rheostat
ii) Wire crossing without joining
Step-by-Step AI Explanation
Verified Method
i) Rheostat: A rectangle with an arrow pointing to the top side or a zigzag line with an arrow crossing it.
ii) Wire crossing without joining: Two lines crossing each other, where one line has a small semi-circular loop over the point of intersection.
Q4short answer1 mark
How many times the magnetic field produced by a circular coil of a conductor having 5 turns is larger than the magnetic field produced by a coil of 1 turn ?
Step-by-Step AI Explanation
Verified Method
The magnetic field produced by a circular coil is directly proportional to the number of turns ($n$). Therefore, a coil with 5 turns produces a magnetic field that is 5 times larger than that produced by a coil of 1 turn.
Q5short answer2 marks
Observe the figure given below. Among the resistors A and B, through which of the resistors more current flows ? Give reason for your answer.
Step-by-Step AI Explanation
Verified Method
In the given circuit, the resistors A ($4\,\Omega$) and B ($20\,\Omega$) are connected in series. In a series combination, the current flowing through every component in the circuit is the same. Therefore, equal current flows through both resistors A and B.
Q6short answer2 marks
What is the colour of danger signal lights ? Why is that colour used ?
Step-by-Step AI Explanation
Verified Method
The colour of danger signal lights is red. Red light is used because it has the longest wavelength in the visible spectrum and is least scattered by air molecules, dust, or smoke particles. This allows the signal to be seen from a long distance, even in foggy or rainy conditions.
Q7short answer2 marks
a) State Fleming’s left hand rule.
b) What is the potential difference between the live wire and the neutral wire in domestic electric circuit in our country ?
Step-by-Step AI Explanation
Verified Method
a) Fleming’s left-hand rule states that if you stretch the thumb, forefinger, and middle finger of your left hand such that they are mutually perpendicular to each other, the forefinger indicates the direction of the magnetic field, the middle finger indicates the direction of current, and the thumb indicates the direction of the force or motion on the conductor.
b) The potential difference between the live wire and the neutral wire in domestic electric circuits in India is 220 V.
Q8long answer3 marks
What is presbyopia ? What are the reasons for this defect ? Suggest a remedy for this defect.
OR
What is short-sightedness ? What are the reasons for this defect ? How can this defect be corrected ?
Step-by-Step AI Explanation
Verified Method
Presbyopia is the defect of vision in which an old person cannot see nearby objects clearly due to the loss of accommodation of the eye. Reasons: This occurs due to the gradual weakening of ciliary muscles and the diminishing flexibility of the crystalline eye lens. Remedy: This defect is corrected by using convex lenses of suitable power (often requiring bifocal lenses).
Q9long answer3 marks
What is fuse ? What are the reasons for causing overload and short circuit in an electric circuit ?
OR
What is earth wire ? Explain the function of the earth wire.
Step-by-Step AI Explanation
Verified Method
Electric fuse: An electric fuse is a safety device used in electrical circuits to protect appliances from damage due to excessive current. It consists of a thin wire made of a material with a low melting point, which melts and breaks the circuit when current exceeds a safe limit.
Reasons for overload: Overloading occurs when too many electrical appliances (especially high-power devices like heaters or ACs) are connected to a single socket or circuit simultaneously, causing the total current to exceed the capacity of the wiring.
Reasons for short circuit: A short circuit occurs when the live wire and the neutral wire come into direct contact with each other, often due to damaged insulation or a fault in an appliance. This leads to a sudden, extremely low-resistance path, causing a massive surge in current.
Q10long answer3 marks
Draw the ray diagram that shows the image formation when an object is kept at ‘C’ of a concave mirror. Write the nature of the image formed.
[ C : Centre of curvature ]
Step-by-Step AI Explanation
Verified Method
For a concave mirror, when an object is placed at the centre of curvature (C):
1. A ray parallel to the principal axis passes through the focus (F) after reflection.
2. A ray passing through the focus (F) emerges parallel to the principal axis after reflection.
Nature of the image formed:
- Real and inverted.
- The size of the image is equal to the size of the object.
- The image is formed at C.
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b) State the laws of reflection of light.
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OR a) What is magnification ? Write the formula used to calculate the magnification of the image produced by a lens. b) State the laws of reflection of light.
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