Physics Exam Paper PDF

## 68/ESS/1-312-C] **20. Fill in the blanks:** (i) In a nuclear reactor, moderator is used to **slow down** the triggering neutrons. (ii) In fission reaction, the energy released is 0.84 MeV/u whereas in fusion reaction, the energy released is **200** MeV/u. **21. Fill in the blanks:** (i) A pho...

## 68/ESS/1-312-C] **20. Fill in the blanks:** (i) In a nuclear reactor, moderator is used to **slow down** the triggering neutrons. (ii) In fission reaction, the energy released is 0.84 MeV/u whereas in fusion reaction, the energy released is **200** MeV/u. **21. Fill in the blanks:** (i) A photodiode is always connected in **reverse** biasing. (ii) A forward biased p-n junction offers **less** resistance to the flow of electrons. **22. Match Column - I statement with the right option of Column - II:** | Column - I | Column - II | |---|---| | Use of a p-n junction diode | (a) Rectifier | | Use of a transistor | (b) Oscillator | **23. Write true for correct statement and false for incorrect statement:** (i) **True** The relation tan) = µ gives an angle at which when a ray is incident, the refracted ray is completely plane polarised. (ii) **False** The intensity of red light scattered by air in the morning is more than the intensity of blue light. **24. Write true for correct statement and false for incorrect statement:** (i) **True** A NOT gate uses two p-n junctions. (ii) **False** When a zener diode is not working on its optimum voltage condition the load draws less power than the power dissipated in the diode. **25. Match Column - I statement with the right option of Column - II:** | Column - I | Column - II | |---|---| | Transistor in common base configuration | (a) Input Output | | Transistor in common emitter configuration | (b) Input Output | **26. Match Column - I statement with the right option of Column - II:** | Column - I | Column - II | |---|---| | Visible spectrum | (b) Balmer series | | Far infrared spectrum | (d) Pfund series | **27. Match Column - I statement with the right option of Column - II.** | Column - I | Column - II | |---|---| | Law of conservation of linear momentum | (c) Ptotal = Constant | | Expression for friction force | (a) F = µR | **28. Fill in the blanks:** (i) Efficiency of a heat engine does not depend on the nature of the **working substance**. (ii) 1 kilo calorie = **4186** J. **29. A body of mass of 50 kg is placed on the smaller piston of a hydraulic lift. If the area of the smaller piston is 0.1 m² and that of the bigger piston is 10 m², calculate the weight of the car which can be lifted by this body.** Let the weight of the car be W. Applying Pascal's law, we have: Pressure on smaller piston = Pressure on bigger piston Therefore, $ \frac{50 \times 9.8}{0.1} = \frac{W }{10} $ Solving for W, we get W = 5000 x 9.8 = **49000 N** **OR / अथवा** **Calculate the excess of pressure inside a soap bubble of radius 4 cm. The surface tension of soap solution is 25×10-3 Nm-1.** The excess pressure inside a soap bubble is given by: $P = \frac{4T}{r} $ where T is the surface tension and r is the radius of the bubble. Substituting the given values, we get: $P = \frac{4\times 25\times 10^{-3}}{4 \times 10^{-2}}$ = **2.5 Pa** **30. Draw the symbol of a:** (i) n-p-n transistor *Symbol of an n-p-n transistor:* ``` --- | | | | | E | C | | | | --- B ``` (ii) p-n-p transistor *Symbol of a p-n-p transistor:* ``` --- | | | | | C | E | | | | --- B ``` **OR / अथवा** **Draw diagrams to show the relative position of energy bonds in:** (i) Semiconductors *Energy band diagram for an intrinsic semiconductor:* ``` Conduction band ----------------- Energy gap (Eg) Valence band ----------------- ``` (ii) Insulator *Energy band diagram for an insulator:* ``` Conduction band ----------------- Energy gap (Eg) Valence band ----------------- ``` Show the magnitude of energy gap in each case: The energy gap for semiconductors is between **0.1 to 3 eV** and the energy gap for insulators is **more than 3 eV**. **31. Give any two differences between the way the electric field and the magnetic field deflect a moving charged particle.** | Feature | Electric Field | Magnetic Field | |---|---|---| | Direction of force | Direction of force is along the electric field | Direction of force is perpendicular to the magnetic field and the velocity of the charge | | Nature of path | The path of the charged particle is parabolic | The path of the charged particle is circular | **OR / अथवा** **Consider a body suspended from a vertical spring. How will the position of the body change when a current is passed through the spring? Explain.** When a current is passed through the spring, the spring will experience a magnetic force. This magnetic force will cause the spring to stretch or compress, depending on the direction of the current. As a result, the position of the body suspended from the spring will also change. This is due to the interaction between the magnetic field generated by the current in the spring and the magnetic field of the Earth. **32. Give the names of the four factors on which the resistance of a conductor depends.** The four factors that affect the resistance of a conductor are: - **Length of the Conductor:** Resistance is directly proportional to the length of the conductor. - **Cross-sectional Area of the Conductor:** Resistance is inversely proportional to the cross-sectional area of the conductor. - **Temperature:** Resistance increases with an increase in temperature for most conductors, except for semiconductors. - **Material of the Conductor:** Different materials have different resistances. **OR / अथवा** **Are the various devices in a household circuit connected in series or in parallel? Why?** The devices in a household circuit are connected in **parallel**. This is because: - **Individual Operation:** Each appliance can be used independently, even if the others are not in use. - **Constant Voltage:** Each appliance receives the same voltage, irrespective of whether other appliances are on or off. - **Safety:** If one appliance fails, the other appliances continue to work because the circuit is not broken. **33. State Stoke's law. Mention any two of its applications.** **Stokes's Law:** When a spherical object moves through a viscous fluid, the viscous force acting on the object is directly proportional to the velocity of the object, the radius of the object, and the viscosity of the fluid. **Applications of Stoke's Law:** - **Sedimentation in liquids:** Determining the sedimentation rate of particles in a liquid, for example, in soil analysis or determining the settling rate of suspended particles in a water treatment plant. - **Determining the Viscosity of Fluids:** Measuring the viscosity of fluids by observing the rate of fall of a spherical object through the fluid. **34. What is meant by:** (i) an isothermal process: An isothermal process is a process where the temperature of the system remains constant. In such a process, heat may be exchanged with the surroundings, but the internal energy of the system remains constant. (ii) an adiabatic process: An adiabatic process is a process where no heat is exchanged between the system and the surroundings. This means that the heat capacity of the system is zero. **35. State de-Broglie's concept of matter waves. Write expression for de-Broglie associated with an electron accelerated through a potential difference of V volts.** **de-Broglie's Hypothesis:** Particles, such as electrons, protons, and neutrons, can exhibit wave-like properties. This concept is known as wave-particle duality. **de-Broglie Wavelength:** The wavelength of a matter wave associated with a particle is given by: $λ = h/p$ where: * λ is the de-Broglie wavelength * h is Planck's constant * p is the momentum of the particle **Expression for de-Broglie Wavelength of an Electron:** The kinetic energy (KE) of an electron accelerated through a potential difference of V volts is: KE = eV where e is the charge of an electron. Also we know that KE = $p^2 / 2m$, where m is the mass of the electron. Therefore, $p = \sqrt{2mKE} = \sqrt{2meV}$. Hence, the de-Broglie wavelength of the electron is given by: **λ = h/p = h / √(2meV)** **36. Distinguish between (i) Pitch and frequency (ii) Loudness and intensity.** (i) Pitch and Frequency: - Pitch refers to the subjective perception of the frequency of sound, determined by the ear. It is the highness or lowness of a sound. - Frequency refers to the rate at which sound waves vibrate, usually expressed in Hertz (Hz). (ii) Loudness and Intensity: - Loudness is the subjective perception of sound intensity, measured in decibels (dB). It is how loud or soft a sound is perceived by a listener. - Intensity is the objective measure of the amount of sound energy passing through a unit area per unit time. It is measured in Watts per square meter (W/m²). **37. Give in brief the principle of working of Parachute.** A parachute works on the principle of air resistance. When a parachute is opened, it increases the surface area of the falling object, resulting in increased air resistance. This resistance slows down the descent of the object, providing a safe landing. **38. Write any three distinguishing features of the fringe patterns formed in Young's double slit experiment and single slit diffraction.** **Young's Double Slit Experiment:** - **Spacing of fringes:** The fringes are evenly spaced and the spacing between them is constant. - **Brightness of fringes:** The fringes are brighter and of almost equal intensity. - **Fringe width:** The fringe width is dependent on the wavelength of light, the distance between the slits, and the distance between the slits and the screen. **Single Slit Diffraction:** - **Central maximum:** The central maximum is wider and brighter than the other secondary maxima. - **Intensity:** The intensity of the secondary maxima decreases as we move away from the central maximum. - **Spacing:** The spacing between the secondary maxima increases as we move away from the central maximum. **OR / अथवा** **In a single slit diffraction experiment how will the angular width of central **maximum** change when:** (i) Slit width is decreased: The angular width of the central **maximum** will increase. When the slit width is decreased, the diffraction pattern spreads out more, resulting in a wider central **maximum**. (ii) The distance between the slit and the screen is increased: The angular width of the central **maximum** will decrease as the distance between the slit and the screen is increased. This is because the diffraction pattern converges as the distance increases. (iii) Light of smaller wavelength is used? Explain. The angular width of the central **maximum** will decrease as the wavelength of light is reduced. This is because the diffraction pattern is more tightly packed for smaller wavelengths, meaning the central **maximum** is narrower. **39. A stationary wave is represented by y= 2 sin (πx/10 ) cos(100πt), where x and y are** **in centimeter. Calculate the distance between a node and adjoining antinode.** The given equation for the stationary wave is: y= 2 sin (πx/10 ) cos(100πt) Comparing this equation with the standard equation for a stationary wave: y = 2A sin(kx) cos(ωt) We can see that the amplitude A = 1 cm, wave number k = π/10, and angular frequency ω = 100π. The distance between a node and an adjoining antinode is half the wavelength. The wavelength is given by: λ = 2π/k = 2π/(π/10) = 20 cm. Therefore, the distance between a node and an adjoining antinode is λ/2 = 20/2 = **10 cm**. **OR / अथवा** **A transverse harmonic wave can be represented by: y = 3 sin (36t + 0.018x )/4 , where y and x are in metre and time t in seconds.** (i) Is it a progressive wave or a stationary wave? y = 3 sin (36t + 0.018x )/4 Since this wave function involves a term of the form (ωt + kx), where ω is the angular frequency and k is the wave number, this wave is **progressive**. (ii) Calculate the: (a) Period of vibration: The angular frequency is ω = 36 rad/s. The period of vibration is given by T = 2π/ω. Therefore, T = 2π/36 = **π/18 seconds**. (b) Wavelength of the wave: The wave number is k = 0.018 rad/m. The wavelength is given by λ = 2π/k. Therefore, λ = 2π/0.018 = **111.11 m**. **40. Define dispersive power of an optical medium. Write a mathematical expression for dispersive power in terms of refractive indices for different colours. Explain why the flint glass prism produces a broader spectrum than that due to a similar crown glass-prism.** **Dispersive Power:** The dispersive power of an optical medium is a measure of its ability to separate different wavelengths of light. It is defined as the ratio of the difference between the refractive indices for two specific wavelengths (e.g., red and violet) to the mean refractive index for those wavelengths. **Mathematical Expression for Dispersive Power:** Let μR, μY, and μV represent the refractive indices of the medium for red, yellow, and violet light, respectively. Then, the dispersive power w is given by: w = (μV - μR)/( μY - 1) **Flint Glass vs. Crown Glass:** Flint glass has a higher dispersive power than crown glass. This is because Flint glass has a higher refractive index for blue light compared to red light. As a result, the difference between the refractive indices for blue light and red light is larger for Flint Glass. Therefore, Flint Glass prisms produce a broader spectrum compared to crown glass prisms. **41. Refracting angle of a prism is **(1/2)°** and refractive index is 1.6. Calculate the value of angle of minimum deviate for the prism in the minute unit of angle.** The angle of minimum deviation (δm) for a prism is related to its refractive index (μ) and the angle A by the formula: (μ-1)A = δm Given: A = (1/2)° = 30' μ = 1.6 Substituting these values into the formula: (1.6 - 1) × 30' = δm 0.6 × 30' = δm δm = **18'** Therefore, the angle of minimum deviation for the prism is 18 minutes.