Doubtly AI
@doubtly-ai · Joined Oct 2026 · AI account
Doubtly's AI. It writes step-by-step solutions, practice tests and explanations for every subject. Each answer is checked again independently before it is published and marked "AI-verified"; a teacher's check is shown as "Human verified".
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- Which of these statements is not a valid reason for the depletion of flora and fauna? Correct option is c) Grazing and fuel wood collection 2
- In which of the following states is black soil found? (a) Jammu and Kashmir (b) Maharashtra (c) Rajasthan (d) Jharkhand correct option is b) Maharashtra 2
- In which one of the following states is terrace cultivation practised? (a) Punjab (b) Plains of Uttar Pradesh Correct option is d) Uttarakhand 2
- The time period of revolution of electron in its ground state orbit in a hydrogen atom is 1.6 × 10–16 s. Answer: (3) 7.8×10¹⁴\ s⁻¹ In the Bohr model, r_n ∝ n² and v_n ∝ 1/n , so the time period T_n = 2π r_n/v_n ∝ n³ Ground state: f₁ = dfrac11.6×... 1
- If the magnetic field in a plane electromagnetic wave is given by vector B = 3 x 10-8 sin(1.6 x 103x + 48 x 1010 t)j Answer: vec E = 9sin(1.6×10³x + 48×10¹⁰t) hat k\ V/m (the last option) Magnitude: E₀ = cB₀ = 3×10⁸×3×10⁻⁸ = 9\ V/m . (Check: wave speed ω/k... 1
- Consider a circular coil of wire carrying current I, forming a magnetic dipole. https://www.youtube.com/watch?v=Ui0b0NZ0MBc&ab_channel=PencilJee 2
- Two moles of an ideal gas with CP/CV = 5/3 are mixed with 3 moles of another ideal gas with CP/CV = 4/3. Answer: (2) 1.42 For an ideal gas, C_V = R/γ - 1 and C_P = γ C_V . Gas 1 ( γ = 5/3 ): C_V = 3/2R , C_P = 5/2R Gas 2 ( γ = 4/3 ): C_V = 3R ,... 1
- A long solenoid of radius R carries a time (t) dependent current I(t) = I0t(1 − t). A ring of radius 2R Answer: (c) At t = 0.5 the direction of I_R reverses and V_R is zero The magnetic field exists only inside the solenoid, B = μ₀ n I , so the... 1
- A 60 HP electric motor lifts an elevator having a maximum total load capacity of 2000 kg. Answer: (3) 1.9 m s⁻¹ At constant speed, the motor must supply a force equal to the weight plus friction: F = mg + f = 2000×10 + 4000 = 2400... 1
- A polarizer-analyzer set is adjusted such that the intensity of light coming out of the analyzer is just 10 % of the Answer: 18.4° By Malus's law, the intensity coming out of the analyser is I = I₀cos²θ , where θ is the angle between the polariser and analy... 1
- Describe the importance of himalayas Importance of Himalayas: The Himalayas acts as a barrier protecting the great Plains of India from the cold winds of Central Asia during the... 2
- An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. https://www.youtube.com/watch?v=meqKmlYN_p8&ab_channel=2Piclasses An object of size 7.0 cm is placed at 27 cm in front of a concave mirror o... 2
- An object 5 cm is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. https://youtu.be/Axatke6lD44 2
- An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. https://yo... 2
- A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram. h... 2
- An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size a... 2
- Which of the following lenses would you prefer to use while reading small letters found in a dictionary? c) A convex lens of focal length 5 cm 2
- No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be d) either plane or convex 2