Tool By Zeal Point

Refraction / Optics - Properties of Light : 2

Q. Who controls the size of the pupil ?

Ans - Iris
Explanation: Iris is the coloured part of the eye. It expands or contracts the pupil depending on light intensity, allowing proper amount of light to enter the eye.

Q. Diameter of the human eye ?

Ans - About 2.3 to 2.5 cm
Explanation: A normal eye is almost spherical with an average diameter close to 2.4 cm, which helps maintain accurate curvature for proper focusing and image formation on the retina.

Q. Which type of lens is in the human eye ?

Ans - Convex lens
Explanation: The eye contains a flexible convex (converging) lens that focuses light rays onto the retina by changing its curvature using ciliary muscles for clear vision at different distances.

Q. Range of vision of a healthy human eye ?

Ans - Infinity
Explanation: A normal eye can see distant objects as if they are at infinity because parallel light rays from far objects focus easily on the retina without extra muscular effort.

Q. Least distance of distinct vision ?

Ans - 25 cm
Explanation: A healthy eye can clearly see nearby objects only beyond 25 cm. Closer objects cause strain because the eye’s lens cannot accommodate enough to form a sharp image.

Q. Type of image formed on the retina ?

Ans – Real, inverted, and diminished
Explanation: The eye’s convex lens focuses light to form a real, upside-down, and smaller image on the retina. The brain then interprets it as upright and correctly oriented.

Q. Lens used to correct myopia ?

Ans- - Concave lens
Explanation: Myopic eyes focus images before the retina. A concave lens diverges incoming light, shifting the image backward so it exactly forms on the retina, restoring clear distant vision.

Q. Lens used to view water depth ?

Ans - Convex lens
Explanation: Convex lenses magnify objects by converging light rays, allowing clearer visibility of underwater objects by correcting distortions caused by refraction at the water surface.

Q. Can myopia be corrected by bifocal lenses ?

Ans - Yes
Explanation: Bifocal lenses contain both concave and convex segments, letting a person with both myopia and hypermetropia see distant and near objects clearly without switching glasses repeatedly.

Q. Defect where near objects appear unclear ?

Ans - Hypermetropia
Explanation: In hypermetropia, the image forms behind the retina due to a short eyeball or weak lens. The person can't see near objects clearly but distant vision remains better.

Q. Colour with minimum diffraction ?

Ans - Red
Explanation: Red light has the longest wavelength, so it bends the least around obstacles or openings, resulting in the smallest diffraction compared to shorter-wavelength colours like blue or violet.

Q. White light contains how many colours ?

Ans - Seven
Explanation: White light splits through a prism into seven colours (VIBGYOR). Each colour has a different wavelength, causing differential refraction and formation of the visible spectrum.

Q. Device used to obtain sunlight spectrum ?

Ans - Prism
Explanation: A prism disperses sunlight into its seven constituent colours by refracting different wavelengths at different angles, producing a clear and observable colour spectrum.

Q. Colour with maximum deviation in spectrum ?

Ans - Violet
Explanation: Violet has the shortest wavelength, so it bends the most when passing through a prism, causing maximum deviation compared to all other colours in white light.

Q. Primary colours of light ?

Ans - Red, Green, Blue
Explanation: These three colours combine in different proportions to produce all other colours of light. Mixing all three in equal amounts produces white light.

Q. Reason for twinkling of stars ?

Ans - Atmospheric refraction
Explanation: Light from stars bends repeatedly due to varying air densities in the atmosphere. This continuous refraction changes brightness and position, making stars appear to twinkle.

Q. Sun appears 4 minutes early due to ?

Ans - Atmospheric refraction
Explanation: Sunlight bends as it enters Earth’s atmosphere. This bending makes the sun appear slightly higher than its actual position, causing sunrise to appear earlier.

Q. Twinkling of stars represents which phenomenon ?

Ans - Atmospheric refraction
Explanation: Uneven refraction of starlight through layers of air with different densities causes variation in brightness, demonstrating the effect of atmospheric refraction.

Q. Which colour scatters the most ?

Ans - Blue
Explanation: Blue light has a shorter wavelength, so atmospheric particles scatter it more strongly. This intense scattering makes the sky appear blue during daytime.

Q. Air molecules scatter which colour most ?

Ans - Blue
Explanation: Tiny air molecules scatter shorter wavelengths like blue far more efficiently than longer wavelengths, causing predominant blue light to reach our eyes from all directions.

Q. Colour with maximum wavelength ?

Ans - Red
Explanation: Red light has the longest wavelength in the visible spectrum, making it scatter and refract the least, which is why it is used in signals for maximum visibility.

Q. Who controls the size of the pupil ?

Ans - Iris
Explanation: Iris is the coloured part of the eye. It expands or contracts the pupil depending on light intensity, allowing proper amount of light to enter the eye.

Q. Diameter of the human eye ?

Q. Which type of lens is in the human eye ?

Q. Range of vision of a healthy human eye ?

Q. Least distance of distinct vision ?

Ans - 25 cm
Explanation: A healthy eye can clearly see nearby objects only beyond 25 cm. Closer objects cause strain because the eye’s lens cannot accommodate enough to form a sharp image.

Q. Type of image formed on the retina ?

Q. Lens used to correct myopia ?

Q. Lens used to view water depth ?

Q. Can myopia be corrected by bifocal lenses ?

Q. Defect where near objects appear unclear ?

Q. Colour with minimum diffraction ?

Q. White light contains how many colours ?

Q. Device used to obtain sunlight spectrum ?

Q. Colour with maximum deviation in spectrum ?

Ans - Violet
Explanation: Violet has the shortest wavelength, so it bends the most when passing through a prism, causing maximum deviation compared to all other colours in white light.

Q. Primary colours of light ?

Ans - Red, Green, Blue
Explanation: These three colours combine in different proportions to produce all other colours of light. Mixing all three in equal amounts produces white light.

Q. Reason for twinkling of stars ?

Q. Sun appears 4 minutes early due to ?

Q. Twinkling of stars represents which phenomenon ?

Q. Which colour scatters the most ?

Ans - Blue
Explanation: Blue light has a shorter wavelength, so atmospheric particles scatter it more strongly. This intense scattering makes the sky appear blue during daytime.

Q. Air molecules scatter which colour most ?

Q. Colour with maximum wavelength ?

Ans - Red
Explanation: Red light has the longest wavelength in the visible spectrum, making it scatter and refract the least, which is why it is used in signals for maximum visibility.

Q. What colour does the sky appear from the Moon ?

Ans - Black
Explanation (30 words):
The Moon has no atmosphere, so sunlight does not scatter as it does on Earth. Without scattering, the sky cannot appear blue and therefore always looks completely black even during daytime.

Q. Scattering of light caused by suspension particles is called -

Ans - Tyndall Effect
Explanation:
The Tyndall effect occurs when tiny particles in a colloid or suspension scatter light passing through it, making the light beam clearly visible. This effect helps distinguish true solutions from colloids.

Q. Which colour in white light has the maximum wavelength ?

Ans - Red
Explanation:
Red light has the longest wavelength among visible colours, allowing it to scatter the least and travel longer distances. This is why red is used for signals and appears last in the spectrum.

Q. How does the sound of an electric device appear ?

Ans - Harsh (Karkash)
Explanation:
Electric devices often produce irregular, high-frequency vibrations due to motors and electromagnetic activity, creating a rough, harsh sound rather than smooth musical tones.

Q. Charge on an electron is -

Ans - 1.6 × 10⁻¹⁹ C
Explanation:
An electron carries a fundamental negative charge of 1.6 × 10⁻¹⁹ coulomb. This smallest unit of charge forms the basis of electric current and all electrostatic interactions.

Q. SI unit of electric charge ?

Ans - Coulomb
Explanation:
One coulomb is defined as the electric charge transported by a current of one ampere in one second. It is the standard SI unit for measuring electric charge.

Q. One microampere equals how much electric current ?

Ans - 10⁻⁶ A
Explanation:
Micro (µ) represents 10⁻⁶. Therefore, one microampere equals one-millionth of an ampere, used for measuring extremely small currents in delicate electronic circuits.

Q. Which instrument is used to measure electric current ?

Ans - Ammeter
Explanation:
An ammeter is designed with very low resistance and is connected in series so the entire current passes through it, allowing accurate measurement of current in a circuit.

Q. What type of current is obtained from a battery ?

Ans - Direct Current (DC)
Explanation:
A battery provides current that flows in one fixed direction—from positive to negative terminal—producing direct current, used in torches, mobiles, and electronic devices.

Q. How is an ammeter connected in a circuit ?

Ans - In series
Explanation:
To measure current, an ammeter must be connected in series so the same current flows through it. Series connection ensures correct measuring without altering circuit behavior.

Q. SI unit of electric current ?

Ans - Ampere
Explanation:
One ampere is defined as the flow of one coulomb of charge per second. It is the standard SI unit of electric current in all circuits and electrical systems.

Q. Which device has no positive or negative sign ?

Ans - Coil (or Galvanometer coil)
Explanation:
A simple coil does not have polarity markings because current can pass in either direction. Only meters like ammeters or voltmeters require polarity signs for proper connection.

Q. A wire carries 120 C charge in 1 minute. Find current.

Ans - 2 Ampere
Explanation:
Current I = Q/t = 120/ 60 =2A. Thus, two coulombs of charge flow each second, producing a current of 2 amperes.

Q. Moving particles in an electric current are -

Ans Electrons
Explanation:
In metals, free electrons move through the conductor when voltage is applied. Their continuous drift constitutes electric current, while protons remain fixed in the atomic structure.

Q. How many protons make 1 coulomb of charge ?

Ans - 6.25 × 10¹⁸ protons
Explanation:
Each proton carries a charge of 1.6 × 10⁻¹⁹ C. Therefore, dividing 1 coulomb by this value gives 6.25 × 10¹⁸ protons required to produce one coulomb of positive charge.

Q. In which case are electrons the moving particles ?

Ans - In electric current through conductors
Explanation:
Metallic conductors contain free electrons that move when potential difference is applied. These moving electrons create the flow of electric current in wires and devices.

Q. Flow of electric charge is called -

Ans - Electric current
Explanation:
Electric current results when charges—mainly electrons—move through a conductor due to a potential difference. Its magnitude depends on how much charge passes per second.

Q. SI unit of potential difference ?

Ans - Volt
Explanation:
One volt is the potential difference when one joule of work is done in moving one coulomb of charge between two points. It measures electrical "pressure."

Q. A voltmeter scale has 0V to 1V with 20 divisions. Least count ?

Ans - 0.05 V
Explanation:
Least count = Total range ÷ number of divisions = 1 ÷ 20 = 0.05 V. This is the smallest measurable voltage on the instrument.

Q. Instrument used to measure potential difference ?

Ans - Voltmeter
Explanation:
A voltmeter has high resistance and is connected in parallel across a component. This ensures it measures voltage without drawing significant current from the circuit.

Q. One volt equals -

Ans - Joule per Coulomb
Explanation:
1 volt = 1 joule of work done to move 1 coulomb of charge. This expresses the relationship between energy transferred and charge moved in an electric field.

Q. Work done in moving 2 coulomb charge across 12 V ?

Ans - 24 Joule
Explanation:
Work W = V × Q = 12 × 2 = 24 joules. This is the energy required to shift the charge through the given potential difference.

Q. Volt (V) is equal to -

Ans - J/C (Joule per Coulomb)
Explanation:
A volt represents how much energy (in joules) is transferred per unit charge (in coulombs). It is the standard measure of potential difference in circuits.

Q. Which of the following is not the same ?

Ans – Joule and Electron
Explanation: A joule is an energy unit; an electron is a fundamental charged particle. They are entirely different physical concepts: one measures energy, the other is a particle carrying charge.

Q. Ohm’s law is represented by -

Ans – V = I·R
Explanation: Ohm’s law states that the potential difference across a conductor is proportional to the current through it; the constant of proportionality is resistance, R (V = IR).

Q. What is the purpose of electromotive force (emf) ?

Answer – To drive and maintain current
Explanation: EMF supplies energy to move charges around a circuit, creating and sustaining current. It raises charge potential, enabling increase or maintenance of current against circuit resistance.

Q. Formula to determine a coil’s resistance ?

Ans - R = V / I
Explanation: Resistance equals voltage across the coil divided by current through it. Measuring V and I lets you calculate R using Ohm’s law for any ohmic component.

Q. Relation between V (potential difference), R (resistance) and I (current) ?

Ans - V = I·R
Explanation: Voltage equals current times resistance. This linear relation holds for ohmic conductors and links electrical “pressure” (V) to charge flow (I) through opposition (R).

Q. A heater coil resistance 55 Ω connected to 220 V: current = ?

Ans - 4 A
Explanation: Using I = V/R gives I = 220/55 = 4 amperes. Thus the heater draws four amps from a 220 V source if its resistance is 55 Ω.

Q. A good conductor of electricity is -

Answer – Silver
Explanation: Silver has the highest electrical conductivity among metals due to its free electron density and low resistivity. Copper is widely used because it’s cheaper and nearly as good.

Q. A conductor’s resistance is -

Ans - Very small
Explanation: Ideal conductors have extremely low resistance, allowing easy charge flow. Practical metallic conductors (like copper or silver) have small but finite resistance determined by material properties and geometry.

Q. Unit of force (SI) -

Ans - Newton (N)
Explanation: Force in SI is measured in newtons. One newton is the force that gives a 1 kg mass an acceleration of 1 m/s² (F = ma).

Q. Which is the best electrical conductor ?

Ans - Silver
Explanation: Silver’s electron mobility and crystal structure yield the lowest resistivity, making it the best conductor; cost and tarnishing limit its widespread electrical use.

Q. Unit of electrical resistance ?

Ans - Ohm (Ω)
Explanation: One ohm is the resistance that allows one ampere of current under one volt potential difference. It’s the SI unit for measuring electrical resistance.

Q. Resistance of a conductor depends on -

Ans - Its length
Explanation: Resistance is directly proportional to length (R ∝ L) and inversely proportional to cross-sectional area; longer conductors provide more collisions, increasing resistance.

Q. Effect of temperature increase on conductor’s resistance ?

Ans - It increases
Explanation: In metallic conductors, higher temperature raises atomic vibrations, increasing electron scattering and thus resistance; temperature coefficient quantifies this behaviour.

Q. SI unit of resistance is -

Ans - Ohm (Ω)
Explanation: Ohm is the SI unit representing electrical resistance. It quantifies how strongly a material opposes electric current.