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The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light (a) is scattered the most by smoke or fog (b) is scattered the least by smoke or fog (c) is absorbed the most by smoke or fog (d) moves fastest in air

Answer: (b) is scattered the least by smoke or fog The wavelength of red colour is the largest thus it can easily be seen from a distance. It... View Article

Which of the following statements is correct regarding the propagation of light of different colours of white light in air? (a) Red light moves fastest (b) Blue light moves faster than green light (c) All the colours of the white light move with the same speed (d) Yellow light moves with the mean speed as that of the red and the violet light

Answer: (c) All the colours of the white light move with the same speed Dispersion occurs due to the different degrees of refraction... View Article

The clear sky appears blue because (a) blue light gets absorbed in the atmosphere (b) ultraviolet radiations are absorbed in the atmosphere (c) violet and blue lights get scattered more than lights of all other colours by the atmosphere (d) light of all other colours is scattered more than the violet and blue colour lights by the atmosphere

Answer: (c) violet and blue lights get scattered more than lights of all other colours by the atmosphere The size of the dust particles and... View Article

Which of the following phenomena of light are involved in the formation of a rainbow? (a) Reflection, refraction and dispersion (b) Refraction, dispersion and total internal reflection (c) Refraction, dispersion and internal reflection (d) Dispersion, scattering and total internal reflection

Answer: (c) Refraction, dispersion and internal reflection A rainbow is regarded as one of the most spectacular light shows observed on the... View Article

A prism ABC (with BC as a base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in Figure. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky? (a) (i) (b) (ii) (c) (iii) (d) (iv)

Answer: (b) (ii) When the prism is reversed, the colours that are noticed after dispersion are: VIBGYOR. As a result, figure (ii) is the... View Article

A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct? (a) The near point of his eyes has receded away (b) The near point of his eyes has come closer to him (c) The far point of his eyes has come closer to him (d) The far point of his eyes has receded away

Answer: (a) The near point of his eyes has receded away Near the point of eye move away for 25 cm in hypermetropia. Hence the person should... View Article

A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power (a) + 0.5 D (b) – 0.5 D (c) + 0.2 D (d) – 0.2 D

Answer: (b) – 0.5 D The person concerned has myopia and requires a concave lens to correct the problem. The required focal length of the lens... View Article

Find out the following in the electric circuit given in Figure (a) Effective resistance of two 8 Ω resistors in the combination (b) Current flowing through 4 Ω resistor (c) Potential difference across 4 Ω resistance (d) Power dissipated in 4 Ω resistor (e) Difference in ammeter readings, if any

Answer: According to the Joules heating effect, heat produces in a resistor is Directly proportional to the square of current for the given... View Article

What is Joule’s heating effect? How can it be demonstrated experimentally? List its four applications in daily life.

Answer: Take three resistors R1, R2 and R3, connect them in parallel to make a circuit as shown in the figure. Use the voltmeter to take... View Article

How will you conclude that the same potential difference (voltage) exists across three resistors connected in a parallel arrangement to a battery?

Answer: Take three resistors R1, R2 and R3, connect them in parallel to make a circuit as shown in the figure. Use the voltmeter to take... View Article

How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistances in series connected to a battery?

Answer: Connect three resistors R1, R2, R3 in series to make the circuit. Use an ammeter to see the changes observed in the current flow.... View Article

What is electrical resistivity of a material? What is its unit? Describe an experiment to study the factors on which the resistance of conducting wire depends.

Answer: Resistivity is an inherent property of a conductor which resists the flow of electric current. The resistivity of each material is... View Article

State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.

Answer: Ohm’s law states that at constant temperature potential difference (voltage) across an ideal conductor is proportional to the... View Article

Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source. (a) Will the bulb in the two circuits glow with the same brightness? Justify your answer. (b) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.

Answer: A circuit is said to be connected in series when the same amount of current flows through the resistors. In such circuits, the voltage... View Article

B1 , B2 and B3 are three identical bulbs connected as shown in Figure. When all the three bulbs glow, a current of 3A is recorded by the ammeter A. i) What happens to the glow of the other two bulbs when the bulb B1 gets fused? ii) What happens to the reading of A1 , A2 , A3 and A when the bulb B2 gets fused? iii) How much power is dissipated in the circuit when all the three bulbs glow together?

Answer: (i) When B1 is fused, there will be no influence on the glow of the other two bulbs, which will remain the same since bulb glowing is... View Article

Why is parallel arrangement used in domestic wiring?

Answer: In household wiring, a parallel design is used to ensure that all appliances receive the same amount of energy. Furthermore, if a... View Article

A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 Ω when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if a resistance of 10 Ω is connected in parallel with this series combination, what change (if any) in current flowing through 5 Ω conductor and potential difference across the lamp will take place? Give reason.

Answer: (1) Let R1 be the resistance of the electric lamp. R2 be the resistance of the conductor. In series total resistance = R1 + R2 = 5 +... View Article

What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 5 A. The reading of the ammeter decreases to half when the length of the wire is doubled. Why?

Answer: The electrical resistivity of a material is the measure of how strongly the material opposes the flow of current. The SI unit of... View Article

How does use of a fuse wire protect electrical appliances?

Answer: An electrical fuse is a low melting point copper or other metal wire that breaks due to heat caused by overvoltage or high load to... View Article

Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2 Ω in series with a combination of two resistors (4 Ω each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2 Ω resistor be the same as that across the parallel combination of 4Ω resistors? Give reason.

Answer: The effective resistance of the combination of two resistors in parallel is, Reff = (4 × 4)/(4 + 4) Reff = 16/8 Reff = 2Ω... View Article

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