Physics Syllabus (JEE Main)
Q. A disk rotates about its axis with an angular velocity of ω. If its radius is doubled while keeping the mass constant, what will be the new moment of inertia?
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Solution
The moment of inertia of a disk is I = (1/2)MR^2. If the radius is doubled, the new moment of inertia becomes I' = (1/2)M(2R)^2 = 4I.
Correct Answer: B — 4I
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Q. A distance is measured as 100 m with an error of 2 m. What is the absolute error?
A.
2 m
B.
0.02 m
C.
0.2 m
D.
20 m
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Solution
The absolute error is given as 2 m.
Correct Answer: A — 2 m
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Q. A diverging lens has a focal length of -10 cm. What is the image distance when the object is placed at 5 cm?
A.
-3.33 cm
B.
-5 cm
C.
3.33 cm
D.
5 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, we have 1/(-10) = 1/v - 1/5. Solving gives v = -3.33 cm.
Correct Answer: A — -3.33 cm
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Q. A door is pushed at its edge with a force of 20 N. If the width of the door is 0.8 m, what is the torque about the hinges?
A.
8 Nm
B.
10 Nm
C.
16 Nm
D.
20 Nm
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Solution
Torque (τ) = Force (F) × Distance (r) = 20 N × 0.8 m = 16 Nm.
Correct Answer: C — 16 Nm
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Q. A door is pushed at its edge with a force of 20 N. If the width of the door is 1 m, what is the torque about the hinges?
A.
10 Nm
B.
20 Nm
C.
30 Nm
D.
40 Nm
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Solution
Torque (τ) = F × d = 20 N × 1 m = 20 Nm.
Correct Answer: B — 20 Nm
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Q. A door is pushed at its edge with a force of 50 N. If the width of the door is 1.2 m, what is the torque about the hinges?
A.
60 Nm
B.
50 Nm
C.
70 Nm
D.
40 Nm
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Solution
Torque = Force × Distance = 50 N × 1.2 m = 60 Nm.
Correct Answer: A — 60 Nm
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Q. A door is pushed at its edge with a force of 50 N. If the width of the door is 1 m, what is the torque about the hinges?
A.
25 Nm
B.
50 Nm
C.
75 Nm
D.
100 Nm
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Solution
Torque (τ) = Force (F) × Distance (r) = 50 N × 1 m = 50 Nm.
Correct Answer: B — 50 Nm
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Q. A double convex lens has a focal length of 10 cm. If it is made of a material with a refractive index of 1.5, what is the radius of curvature of each surface assuming they are equal?
A.
15 cm
B.
20 cm
C.
25 cm
D.
30 cm
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Solution
Using the lens maker's formula, R = 2f(n-1) = 2*10*(1.5-1) = 20 cm.
Correct Answer: B — 20 cm
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Q. A double convex lens has a radius of curvature of 20 cm on both sides. What is its focal length if the refractive index is 1.5?
A.
10 cm
B.
15 cm
C.
20 cm
D.
25 cm
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Solution
Using the lens maker's formula, f = R/(n-1), we find f = 20/(1.5-1) = 40 cm.
Correct Answer: A — 10 cm
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Q. A drop of liquid is in equilibrium on a surface. What is the condition for the drop to remain in equilibrium?
A.
Weight equals surface tension
B.
Weight equals gravitational force
C.
Surface tension equals gravitational force
D.
Surface tension equals buoyant force
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Solution
For a drop to remain in equilibrium, the upward force due to surface tension must balance the downward gravitational force.
Correct Answer: C — Surface tension equals gravitational force
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Q. A drop of liquid is spherical in shape. This is due to which of the following?
A.
Gravity
B.
Surface tension
C.
Viscosity
D.
Pressure
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Solution
The spherical shape of a liquid drop is due to surface tension, which minimizes the surface area for a given volume.
Correct Answer: B — Surface tension
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Q. A drop of oil spreads on water instead of sinking. This is due to:
A.
Higher density of oil
B.
Lower surface tension of oil
C.
Higher surface tension of water
D.
Lower viscosity of oil
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Solution
The drop of oil spreads on water because the surface tension of water is higher than that of oil, causing the oil to spread out.
Correct Answer: C — Higher surface tension of water
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Q. A drop of water is spherical in shape due to which property?
A.
Viscosity
B.
Surface tension
C.
Capillarity
D.
Density
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Solution
A drop of water is spherical due to surface tension, which minimizes the surface area.
Correct Answer: B — Surface tension
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Q. A fiber optic cable uses total internal reflection to transmit light. What is the primary requirement for this to work effectively?
A.
The core must have a higher refractive index than the cladding
B.
The cladding must have a higher refractive index than the core
C.
The light must be monochromatic
D.
The cable must be straight
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Solution
For total internal reflection to occur in a fiber optic cable, the core must have a higher refractive index than the cladding.
Correct Answer: A — The core must have a higher refractive index than the cladding
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Q. A fiber optic cable uses total internal reflection. If the refractive index of the core is 1.5 and that of the cladding is 1.4, what is the critical angle?
A.
42.0°
B.
48.6°
C.
60.0°
D.
30.0°
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Solution
Critical angle θc = sin⁻¹(n2/n1) = sin⁻¹(1.4/1.5) ≈ 42.0°.
Correct Answer: A — 42.0°
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Q. A fiber optic cable uses total internal reflection. If the refractive index of the core is 1.6 and the cladding is 1.5, what is the critical angle?
A.
38.7°
B.
41.8°
C.
48.6°
D.
60.0°
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Solution
Critical angle θc = sin⁻¹(n2/n1) = sin⁻¹(1.5/1.6) ≈ 38.7°.
Correct Answer: A — 38.7°
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Q. A fiber optic cable uses total internal reflection. What is the minimum refractive index required for the core if the cladding has a refractive index of 1.45?
A.
1.50
B.
1.45
C.
1.60
D.
1.75
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Solution
For total internal reflection, the core must have a higher refractive index than the cladding, so it must be greater than 1.45.
Correct Answer: A — 1.50
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Q. A fiber optic cable uses total internal reflection. What is the role of the cladding in this context?
A.
To increase the speed of light.
B.
To provide structural support.
C.
To ensure light remains within the core.
D.
To change the wavelength of light.
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Solution
The cladding has a lower refractive index than the core, ensuring that light remains within the core by total internal reflection.
Correct Answer: C — To ensure light remains within the core.
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Q. A fiber optic cable uses total internal reflection. What is the role of the cladding?
A.
To increase the refractive index.
B.
To decrease the refractive index.
C.
To prevent light loss.
D.
To enhance light absorption.
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Solution
The cladding has a lower refractive index than the core, ensuring that light is kept within the core through total internal reflection.
Correct Answer: C — To prevent light loss.
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Q. A figure skater pulls in her arms while spinning. What happens to her angular momentum?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Becomes zero
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Solution
Angular momentum is conserved; it remains constant, but her angular velocity increases.
Correct Answer: C — Remains constant
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Q. A figure skater pulls in her arms while spinning. What happens to her angular velocity?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
By conservation of angular momentum, if the moment of inertia decreases, the angular velocity must increase.
Correct Answer: A — Increases
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Q. A figure skater spins with arms extended. When she pulls her arms in, what happens to her angular momentum?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
Angular momentum remains the same; however, her angular velocity increases due to a decrease in moment of inertia.
Correct Answer: C — Remains the same
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Q. A figure skater spins with arms extended. When she pulls her arms in, what happens to her rotational speed?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
Pulling her arms in decreases her moment of inertia, causing her rotational speed to increase to conserve angular momentum.
Correct Answer: A — Increases
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Q. A figure skater spins with arms extended. When she pulls her arms in, what happens to her angular velocity?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
By conservation of angular momentum, pulling arms in decreases moment of inertia, thus increasing angular velocity.
Correct Answer: A — Increases
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Q. A fluid with a viscosity of 0.1 Pa·s flows through a pipe of radius 0.05 m. If the pressure difference across the pipe is 1000 Pa, what is the flow rate?
A.
0.01 m³/s
B.
0.02 m³/s
C.
0.03 m³/s
D.
0.04 m³/s
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Solution
Using Poiseuille's law, the flow rate Q = (π * r^4 * ΔP) / (8 * η * L). Assuming L = 1 m, Q = (π * (0.05)^4 * 1000) / (8 * 0.1 * 1) = 0.01 m³/s.
Correct Answer: A — 0.01 m³/s
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Q. A fluid with a viscosity of 0.1 Pa·s flows through a pipe of radius 0.05 m. What is the shear stress if the flow rate is 0.01 m³/s?
A.
0.4 Pa
B.
0.2 Pa
C.
0.1 Pa
D.
0.5 Pa
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Solution
Using the formula for shear stress, τ = (4 * η * Q) / (π * r^3), we find τ = 0.4 Pa.
Correct Answer: A — 0.4 Pa
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Q. A fluid with a viscosity of 0.1 Pa·s flows through a pipe of radius 0.05 m. What is the shear stress if the flow velocity is 1 m/s?
A.
0.1 Pa
B.
0.2 Pa
C.
0.4 Pa
D.
0.5 Pa
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Solution
Shear stress = viscosity × (velocity/radius) = 0.1 × (1/0.05) = 2 Pa.
Correct Answer: B — 0.2 Pa
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Q. A flywheel has a moment of inertia I and is rotating with an angular velocity ω. If a torque τ is applied for time t, what is the final angular velocity?
A.
ω + (τ/I)t
B.
ω - (τ/I)t
C.
ω + (I/τ)t
D.
ω - (I/τ)t
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Solution
Using the equation ω_f = ω + αt, where α = τ/I, we get ω_f = ω + (τ/I)t.
Correct Answer: A — ω + (τ/I)t
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Q. A flywheel has a moment of inertia I and is rotating with an angular velocity ω. If a torque τ is applied to it, what is the angular acceleration α?
A.
τ/I
B.
I/τ
C.
Iω/τ
D.
τω/I
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Solution
From Newton's second law for rotation, τ = Iα, thus α = τ/I.
Correct Answer: A — τ/I
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Q. A flywheel is rotating at 1000 rpm. If it is brought to rest in 10 seconds, what is the average angular deceleration?
A.
100 rad/s²
B.
10 rad/s²
C.
20 rad/s²
D.
50 rad/s²
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Solution
First convert rpm to rad/s: 1000 rpm = (1000 * 2π)/60 rad/s. Then use α = (ωf - ωi)/t = (0 - (1000 * 2π)/60) / 10.
Correct Answer: C — 20 rad/s²
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