Physics
Question from maharashtra board physics book of 11th maharashtra board
- A wire of resistance R is stretched uniformly until its length is doubled. Its new resistance is Answer: C. 4R Volume constant: A→ A/2 . R=ρl/A→ρ2l/A/2=4R . 1
- A parallel plate capacitor has capacitance \(C\) with air between the plates. A dielectric slab of dielectric constant 4 and thickness equal to half the plate separation is inserted between the plates. The new capacitance is Answer: B. 1.6 C C'=ε₀A/d-t+t/K=ε₀A/d/2+d/8=8/5·ε₀A/d=1.6C . 1
- The energy stored in a 10 μF capacitor charged to 100 V is Answer: A. 0.05 J U=1/2CV²=1/2×10⁻⁵×10⁴=0.05 J. 1
- Capacitors of 3 μF and 6 μF are connected in series across a 90 V supply. The potential difference across the 3 μF capacitor is Answer: A. 60 V C_s=2 μF, Q=180 μC, V₃=180/3=60 V. 1
- A planet has the same mean density as the earth but twice its radius. If the escape speed on earth is 11.2 km/s, the escape speed on the planet is Answer: A. 22.4 km/s v_e=√(2GM/R)=R√(8π Gρ/3)∝ R for equal density, so 2×11.2=22.4 km/s. 1
- At what height above the earth's surface does the acceleration due to gravity become one-fourth of its value on the surface? (R = 6400 km) Answer: A. 6400 km g/4=g/(1+h/R)²⇒1+h/R=2⇒ h=R . 1
- Blocks of mass 2 kg and 3 kg are in contact on a frictionless horizontal surface. A horizontal force of 10 N is applied to the 2 kg block. The contact force between the blocks is Answer: C. 6 N a=10/5=2 m/s²; force on 3 kg block =3×2=6 N. 1
- A ball of mass 0.15 kg moving at 20 m/s is hit straight back with the same speed. If the contact lasts 0.01 s, the average force on the ball is Answer: C. 600 N Δ p=0.15×40=6 N s; F=6/0.01=600 N. 1
- A projectile is fired so that its horizontal range equals its maximum height. The angle of projection with the horizontal is Answer: C. tan⁻¹(4) 2u²sinθcosθ/g=u²sin²θ/2g⇒tanθ=4 . 1
- A convex lens of focal length 20 cm is placed in contact with a concave lens of focal length 40 cm. The combination behaves as a Answer: D. convex lens of focal length 40 cm 1/F=frac120-frac140=frac140 ; positive, so converging, F = 40 cm. 1
- The critical angle for light going from glass (\(\mu=1.5\)) to air is Answer: B. sin⁻¹(2/3) sin C=frac1μ=2/3 . 1
- A source of frequency 900 Hz moves towards a stationary observer at 34 m/s. If the speed of sound is 340 m/s, the frequency heard is Answer: A. 1000 Hz n'=nv/v-v_s=900×340/306=1000 Hz. 1
- 100 g of water at 80 °C is mixed with 200 g of water at 20 °C. Neglecting heat losses, the final temperature is Answer: D. 40 °C 100(80-T)=200(T-20)⇒ T=40 °C. 1
- Derive the formula for kinetic energy of a particle having mass m and velocity v using dimensional analysis Kinetic energy of a body depends upon mass (m) and velocity (v) of the body. Let K.E. ∝ m^x v^y ∴ K.E. = km^x v^y …….. (1) where, k = dimens... 1
- Describe what is meant by significant figures and order of magnitude. Significant figures: Significant figures in the measured value of a physical quantity is the sum of reliable digits and the first uncertain... 1
- Give your suggestions in two sentences. How you will cheer up one of your lonely classmates. I can cheer up my lonely classmate by giving him/her company and involving in some activities together. We can sit together in the classroom... 1
- “Girls are quiet and like to play nurse”. Do you Agree or Disagree? Justify your answer. I do not agree to the statement. There is no hard and fast rule about this impression about girls. There may be many boys who are very quiet... 1