Physics Class 10 Board Exam - 10 Most Probable Questions

Physics Class 10 Board Exam - 10 Most Probable Questions: The five topics from Physics in the NCERT Class 10 Science textbooks are light, the human eye, electricity, the “magnetic effects of electric current”, and sources of energy. Questions are asked from each of these in the exam with certain types of questions asked repeatedly through the years. Once all concepts are clear, you can fine-tune your preparation for the board exams by focussing on the areas that are tested on most often.

So let's discuss these chapters with important concepts and two most probable questions for class 10 board exam.

Light: Reflection and Refraction

These are the most important concepts in this section:

• Light is a form of electromagnetic radiation that travels in straight lines, unless it encounters an obstacle or a change in the medium through which it is travelling. Mirrors and lenses are both able to form images of objects by reflecting or refracting light. Images can be either real or virtual, depending on the position of the object relative to the mirror or lens.

• The reflecting surfaces of all types, including mirrors, obey the laws of reflection. These laws describe the angle at which light is reflected off a surface and the angle at which it is incident on the surface. The refracting surfaces, including lenses, obey the laws of refraction. These laws describe how light is bent, or refracted, as it passes through a medium with a different index of refraction.

• The mirror formula and the lens formula are equations that describe the relationship between the object distance, image distance, and focal length of a spherical mirror or lens. The mirror formula is 1/u + 1/v = 1/f, where u is the object distance, v is the image distance, and f is the focal length. The lens formula is 1/v - 1/u = 1/f, where u, v, and f have the same meanings as in the mirror formula.

• The power of a lens is a measure of its ability to refract light. It is defined as the reciprocal of the focal length of the lens, and is expressed in units of diopters. The higher the power of a lens, the stronger its refracting ability.

• The refractive index of a transparent medium is a measure of how much the speed of light is slowed down as it passes through the medium. It is defined as the ratio of the speed of light in vacuum to the speed of light in the medium. The refractive index of a medium is an important factor in determining how much light is refracted as it passes through the medium.

• In the case of a rectangular glass slab, refraction occurs at both the air-glass interface and the glass-air interface. The emergent ray is parallel to the direction of the incident ray. This is known as total internal reflection.

Given below are the two most probable questions from this chapter.

Q-1:

1. What do you mean by reflection and reflection of light? Show the difference with a ray diagram of light with convex and concave mirrors and also show the same with a spherical lens.

2. Complete the following ray diagram:

Find the nature, position, and size of the image formed.

Use the mirror formula to determine the magnification in this case.

Q-2:

(a)Define the following terms :

(i) Power of a lens

(ii) Principal focus of a concave mirror

(b) Write the relationship between the object distance (u), image distance (v), and the focal length (f) of a

(i) Spherical lens

(ii) Spherical mirror

(c) An object is placed at a distance of 10 cm from the optical centre of a convex lens of focal length 15 cm. Draw a labelled ray diagram to show the formation of image in this case.

Human Eye And Colourful World

These are the most important concepts:

• The eye is able to adjust its focal length, or the distance at which it can focus on objects clearly, by changing the shape of the lens through a process called accommodation. This allows us to see both near and distant objects clearly.

• The near point of the eye, also known as the “least distance of distinct vision”, is the smallest distance at which the eye can see objects clearly without strain. For a young adult with normal vision, this distance is about 25 cm.

• There are several common refractive defects of vision, including myopia (nearsightedness), hypermetropia (farsightedness), and presbyopia. Myopia is corrected with a concave lens, while hypermetropia is corrected with a convex lens. Presbyopia is a natural ageing process in which the lens of the eye becomes less flexible, making it harder to focus on objects that are close.

• Dispersion is the process of splitting white light into its component colours. This is what causes the colours of the rainbow when light passes through a prism or a water droplet. Scattering of light is the process by which light is reflected or absorbed by particles in the air or in the atmosphere. This is what causes the blue colour of the sky and the reddening of the sun at sunrise and sunset.

Given below are the two most important questions from the chapter.

Q-3:

1. What are the different types of defects of vision and how are these defects corrected? draw a ray diagram to show the position and nature of the image formed in different defects of our eyes.

2. If the near point of the eye of a person is 50 cm, find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye.

Q-4:

Give reasons :

(a) Red colour is selected for danger signals.

(b) The sky appears dark in space.

(c) The time difference between actual sunset and apparent sunset is about 2 minutes.

(d) How is a rainbow formed?

(e) Why do stars twinkle?

(f) Why does the sky appear dark instead of blue to an astronaut?

(g) What happens with light when it passes through a prism explained with a ray diagram.

Electricity

Some important concepts are given below.

• An electric current is a stream of electrons moving through a conductor, and the direction of the current is conventionally taken to be opposite to the direction of the flow of electrons. The SI unit of electric current is the ampere (A).

• To set the electrons in motion in an electric circuit, we use a cell or a battery. A cell generates a potential difference, or voltage, across its terminals. This is measured in volts (V).

• Resistance is a property that resists the flow of electrons in a conductor. It controls the magnitude of the current and is measured in ohms (Ω). Ohm's law states that the potential difference across the ends of a resistor is directly proportional to the current through it, provided the temperature of the resistor remains the same.

• The resistance of a conductor depends on its length, cross-sectional area, and the material of the conductor. The equivalent resistance of several resistors in series is equal to the sum of their individual resistances, while the equivalent resistance of a set of resistors connected in parallel is given by the formula 1/Rp = 1/R1 + 1/R2 + 1/R3 + ...

• The electrical energy dissipated in a resistor is given by the formula W = V × I × t, where W is the energy, V is the voltage, I is the current, and t is the time. The unit of power is the watt (W), which is equal to 1 joule per second. The commercial unit of electrical energy is the kilowatt hour (kWh), which is equal to 3.6 million joules.

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These are the two questions that come most often in the board exam.

Q-5:

(a) State Ohm’s Law.

(b) How is an ammeter connected in an electric circuit?

(c) The power of a lamp is 100 W. Find the energy consumed by it in 1 minute.

(d) A wire of resistance 5 is bent in the form of a closed circle. Find the resistance between two points at the ends of any diameter of the circle.

Q-6:

Draw a schematic diagram of a circuit consisting of a battery of 3 cells of 2V each, a combination of three resistors of 10, 20, and 30 connected in parallel, a plug key, and an ammeter, all connected in series. Use this circuit to find the value of the following :

(a) Current through each resistor

(b) Total current in the circuit

(c) Total effective resistance of the circuit

Magnetic Effects of Electric Current

Following are some important concepts for this chapter.

• A compass needle is a small magnet that is used to determine the direction of magnetic north. The end of the needle that points towards north is called the north pole, while the other end that points towards south is called the south pole.

• Magnetic fields are created by magnets and are regions in which the force of the magnet can be detected. The pattern of the magnetic field around a magnet or a conductor carrying an electric current can be represented using field lines, which are paths along which a hypothetical free north pole would tend to move. The direction of the magnetic field at a point is given by the direction that a north pole placed at that point would take. Field lines are shown closer together where the magnetic field is stronger.

• A metallic wire carrying an electric current has a magnetic field associated with it. The field lines around the wire consist of concentric circles whose direction is given by the right-hand rule. The pattern of the magnetic field around a conductor depends on the shape of the conductor. The magnetic field of a solenoid carrying a current is similar to that of a bar magnet.

• An electromagnet is a magnet that is created by the flow of electric current through a coil of wire. It consists of a core of soft iron wrapped with a coil of insulated copper wire. When a current-carrying conductor is placed in a magnetic field, it experiences a force due to the interaction between the magnetic field and the magnetic field of the conductor. This force is perpendicular to both the field and the current and is given by Fleming's left-hand rule. This principle is the basis of an electric motor, which is a device that converts electrical energy into mechanical energy.

• Electromagnetic induction is the process of producing an induced current in a coil due to a change in the magnetic field around the coil. This change can be due to the relative motion between the coil and a magnet or due to a change in the current through a conductor near the coil. The direction of the induced current is given by Fleming's right-hand rule. A generator is a device that converts mechanical energy into electrical energy by using the principles of electromagnetic induction.

• In most households, we receive alternating current (AC) electric power with a voltage of 220 V and a frequency of 50 Hz. The supply typically consists of three wires: a live wire with red insulation, a neutral wire with black insulation, and an earth wire with green insulation. The potential difference between the live wire and the neutral wire is 220 V.

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These are the two questions that typically come in exams.

Q-7:

(a) Draw the pattern of magnetic field lines due to a magnetic field through and around a current-carrying circular loop.

(b) Name and state the rule to find out the direction of the magnetic field inside and around the loop.

Q-8:

(a) What is an electromagnet? List any two uses.

(b) Draw a labelled diagram to show how an electromagnet is made.

(c) State the purpose of the soft iron core used in making an electromagnet.

(d) List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.

(e) Write the mathematical expression for Joule's law of heating.

(f) Compute the heat generated while transferring 96000 coulombs of charge in two hours through a potential difference of 40W.

Source Of Energy

Following are some concepts from this chapter.

• As our standard of living increases, our energy requirements also increase. In order to meet these energy requirements, we need to improve the efficiency of energy usage and explore new sources of energy.

• Conventional sources of energy, such as fossil fuels, are non-renewable and are in danger of being depleted. Therefore, it is important to look for new sources of energy that are renewable and sustainable.

• The choice of an energy source depends on several factors, including the ease and cost of extracting energy from the source, the efficiency of the technology available for using that source of energy, and the environmental impact of using that source.

• Many of the sources that we use ultimately derive their energy from the Sun, either directly or indirectly. Solar energy, for example, is a renewable source that is obtained directly from the Sun. Other sources of energy, such as wind, hydropower, and biomass, are derived from the Sun's energy indirectly.

These two questions are very important from the board exam perspective.

Q-9

1. Write the energy conversion that takes place in a hydropower plant.

2. Name any two elements that are used in fabricating solar cells.

3. Name the component of sunlight which facilitates drying of wheat after harvesting.

4. List two merits of solar cells.

Q-10:

Name the process used to harness nuclear energy these days. Explain it briefly. List two advantages of using nuclear energy in place of fossil fuels.