NEB Class 11 Science Physics Question Paper 2078

A metre rule is used to measure the length of a piece of string in a certain experiment. It is found to be 20 cm long to the nearest millimeter. How should this result be recorded in a table of results?

Forces are applied to a rigid body. The forces all act in the same plane. In which diagram is the body in equilibrium?

An athlete makes a long jump and follows a projectile motion. Air resistance is negligible. Which one of the following statements is true about the athlete?

At Kulekhani-I Hydro-power station, water flows from Indra Sarowar into the turbines that are a vertical distance of 550 m below the lake, as shown in the diagram. Generally, 780 000 kg of water flows into the turbines every minute. The turbines have the efficiency of 85%. What is the output power of the turbines?

Graphs of stress-strain for four different materials are shown below. Which graph represents the stiffest material?

A boy walks towards a stationary plane mirror at a speed of $1.2\,\text{ms}^{-1}$. What is the relative speed of approach of the boy and his image?

The critical angle between an equilateral prism and air is $45^\circ$. What happens to the incident ray perpendicular to the refracting surface?

In the formation of a rainbow, the light from the sun on water droplets undergoes which of the following phenomenon/phenomena?

In what unit is the power of a lens measured?

A piece of wire of resistance R is bent through $180^\circ$ at mid-point and the two halves are twisted together. What is the resistance of the wire thus formed?

What are the elementary particles with half spin called?

(a) State the law of conservation of momentum. $[2]$

(b) A jumbo jet of mass $4\times10^5\,\text{kg}$ travelling at a speed of 5000 m/s lands on the airport. It takes 2 minutes to come to rest. Calculate the average force applied by the ground on the aeroplane. $[2]$

(c) After landing the aeroplane's momentum becomes zero. Explain how the law of conservation holds here. $[1]$

OR

(a) State Hooke's law. $[2]$

(b) The walls of the tyres on a car are made of a rubber compound. The variation with stress of the strain of a specimen of this rubber compound is shown in Fig. 1.2. As the car moves, the walls of the tyres bend and straighten continuously. Use Fig. 1.2 to explain why the walls of the tyres become warm. $[3]$

(a) What is meant by specific latent heat of vaporization of water $=2.26\,\text{MJ kg}^{-1}$? $[1]$

(b) A 1.0 kW kettle contains 500 g of boiling water. Calculate the time needed to evaporate all the water in the kettle. (Specific latent heat of vaporization of water $=2.26\,\text{MJ kg}^{-1}$). $[3]$

(c) Explain why the actual time needed is a little longer than the time calculated in (b). $[1]$

(a) State any three properties of an ideal gas as assumed by the kinetic theory of gas. $[3]$

(b) A student needed to use the ideal gas for a certain experiment. But, the ideal gas does not exist. Suggest what two different things this student could do to solve his problem. $[2]$

(a) Define temperature gradient in an object. $[1]$

(b) An electric kitchen range has a total wall area of $1.40\,\text{m}^2$ and is insulated with a layer of fibre glass at $175^\circ C$ inner and $35^\circ C$ outer surface. The fibre glass has thermal conductivity $0.040\,\text{Wm}^{-1}\text{K}^{-1}$. Calculate the rate of flow of heat through the insulation (treat fibre as a flat slab of area $1.40\,\text{m}^2$). $[3]$

(c) How might the rate of conduction be affected if the fibre absorbs moisture? Justify your answer. $[1]$

Figure 5.1 shows a ray of light entering and emerging through a part of a convex lens.

(i) Define 'convex lens', and state one daily application of it. $[2]$

(ii) Explain why this lens is also called converging lens. $[1]$

(iii) Calculate the refractive index of the material of the lens shown in the figure. $[2]$

OR

(a) Define 'concave mirror' and state one daily application of it. $[2]$

(b) A certain projector uses a concave mirror that produces an image 5 times bigger than the object, with the screen 5 m away from the mirror (Fig. 5.2).

(i) Give reason why the image is larger than the object. $[1]$

(ii) Calculate the focal length of the mirror. $[2]$

(a) Sketch an electric field pattern around two identical negative point charges. $[2]$

(b) Obtain an equation, in terms of $Q$ and $r$, for the field strength at point X due to two charges shown in Fig. 6.1. $[3]$

(a) Define capacitance of a parallel plate capacitor and state one application of it in an electric circuit. $[2]$

(b) Three capacitors each of $1000\,\mu F$ are connected in an electric circuit as shown below (Fig. 7.1).

(i) Identify the type of combination shown in Fig. 7.1, and calculate the effective capacitance of the combination. $[1+2]$

(a) What is meant by power of a heater is 2 kW? $[1]$

(b) Calculate the resistance of the above-mentioned heater when it is connected to 220 V source. $[2]$

(c) Suggest what changes must be done to the heater so that it gives more heat. Justify your answer. $[2]$

A box at rest is accelerated by a rope attached to a motor. The velocity-time graph below shows the pattern of its motion for 20 s.

(a) If the box is pulled with constant unbalanced force 10 N, show that the initial acceleration of the box is $2.5\,\text{ms}^{-2}$, and calculate its mass. $[2+1]$

(b) After 2.0 seconds the box is being pulled by a constant force 12 N. Determine the size of frictional force acting on the box at this time. $[2]$

(c) Determine the distance the box travels along the ground at 8.0 s. $[3]$

A boy is operating a remote-controlled toy car on a horizontal circular track of radius $1.8\,\text{m}$; the car travels at constant speed.

(i) Explain why the car is accelerating, even though it is travelling at a constant speed. $[2]$

(ii) The car has mass $0.50\,\text{kg}$. The boy increases the speed to $6.0\,\text{ms}^{-1}$. The total radial friction between car and track has a maximum value of $7.0\,\text{N}$. Show by calculation that the car cannot continue to travel in a circular path. $[3]$

(iii) The car is now placed on a track which includes a raised section (Fig. 10.2), an arc of a circle of radius $r=0.85\,\text{m}$. The car loses contact with the raised section if its speed exceeds $v_{max}$. Show that $v_{max}=\sqrt{rg}$. $[3]$

OR

Juno is a NASA orbiter in an elliptical orbit around Jupiter (see figure). The gravitational potential at point A in the orbit of Juno is $-1.70\times10^9\,\text{J kg}^{-1}$.

(a) State what is meant by a gravitational potential at point A is $-1.70\times10^9\,\text{J kg}^{-1}$. $[2]$

(b) At point B, Juno is $1.69\times10^8\,\text{m}$ from the centre of Jupiter. If the mass of Jupiter is $1.90\times10^{27}\,\text{kg}$, calculate the gravitational potential at point B. $[3]$

(c) The mass of Juno is $1.6\times10^3\,\text{kg}$. Determine the change in gravitational potential energy if Juno moves from Point A to Point B. $[3]$

(a) Explain how Rutherford's $\alpha$-scattering experiment suggested that the nucleus of an atom is very small, very dense and positively charged. $[3]$

(b) Considering that the $\alpha$-particles carry average kinetic energy of $2.00\times10^{-10}\,\text{J}$ (as printed), calculate the maximum size of the gold nucleus. [Atomic number of gold is 79 and $e=1.60\times10^{-19}\,\text{C}$] $[3]$

(c) Explain why the radius of the gold nucleus must be much smaller than the value calculated in (b) above. $[2]$