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A person suffering from myopia (near-sightedness) was advised to wear corrective lens of power – 2·5 D. A spherical lens of same focal length was taken in the laboratory. At what distance should a student place an object from this lens so that it forms an image at a distance of 10 cm from the lens?

Power of lens, P = −2.5D Image distance, v = −10cm We have to find object distance from the lens, u. Solution: From the magnification formula,... View Article

Calculate the focal length of a lens, if its power is – 2·5 D.

The power of a lens is the measure of the degree of convergence or divergence of the light rays falling on it. The degree of convergence or... View Article

Calculate the refractive index of the material of a glass slab. Given that the speed of light through the glass slab is 2 8 10^8 m/s and in air is 3 * 10^8 m/s.

Given speed of light through the glass slab is 2 x 108 m / s. The speed of light in the air is 3 x 108 m/s. We need to find the refractive index... View Article

Draw a labelled ray diagram to show the path of a ray of light incident obliquely on one face of a glass slab.

i is the angle of incidence and e is the angle of emergence. i=e and r1=r2 So, the incident ray and the emergent ray are parallel... View Article

Two resistors X and Y of resistances 2 Ω and 3 Ω respectively are first joined in parallel and then in series. In each case the voltage supplied is 5 V. (i) Draw circuit diagrams to show the combination of resistors in each case. (ii) Calculate the voltage across the 3 Ω resistor in the series combination of resistors.

(i) (ii) Given: The resistance of X = R1 = 2Ω The resistance of Y = R2 = 3Ω Voltage, V = 6V To find The voltage across the 3Ω resistor in... View Article

Two lamps rated 100 W, 220 V and 10 W, 220 V are connected in parallel to 220 V supply. Calculate the total current through the circuit.

Power of 1st lamp, P1 = 100W, Voltage of 1st lamp, V1 = 220V Power of 2nd lamp, P2 = 10W, Voltage of 2nd lamp, V2 = 220V To find: Total... View Article

We can develop new plants from the leaves of Bryophyllum. Comment.

Yes, we can develop new plants from the leaves of Bryophyllum. New Bryophyllum plants are reproduced through the vegetative propagation method... View Article

Name the mode of reproduction of the following organisms and state the important feature of each mode: (i) Planaria (ii) Hydra (iii) Rhizopus

(a) (i) Planaria: It has the ability to regenerate the complete body from its cut body parts. Regeneration is the type of asexual reproduction... View Article

Based on the given diagram answer the questions given below. (a) Label the parts A, B, C and D. (b) Name the hormone secreted by testis and mention its role. (c) State the functions of B and C in the process of reproduction.

A: Ureter, B: Seminal Vesicle, C: Urethra D: Vas Deferens. (b) Testosterone is the hormone secreted by the testis. The functions of the male... View Article

Give reasons: (a) Ventricles have thicker muscular walls than atria. (b) Transport system in plants is slow. (c) Circulation of blood in aquatic vertebrates differs from that in terrestrial vertebrates. (d) During the daytime, water and minerals travel faster through xylem as compared to the night. (e) Veins have valves whereas arteries do not.

(a) Ventricles have thicker muscular walls than atria because ventricles have to pump the blood with higher pressure to make it reach different... View Article

State the role of alkaline KMnO4 in the reaction involving conversion of an alcohol to corresponding carboxylic acid.

The role of alkaline KMnO4 in the reaction involving conversion of an alcohol to corresponding carboxylic acid is that it is used as an oxidizing... View Article

‘‘A compound ‘X’ on combustion gives a yellow flame with lots of smoke.’’ What inference would you draw from this statement?

Unsaturated hydrocarbons like ethyne produce a yellow flame when burnt in oxygen due to incomplete combustion in air. The percentage of carbon is... View Article

Define isomerism. Draw all possible isomers of butane.

When two or more organic compounds have the same molecular formula but different structural formula, then the compounds are called isomers and... View Article

How are broken railway tracks joined? Give the name of the process and the chemical equation of the reaction involved.

Broken railway tracks are joined by filling in the gaps with molten iron formed in the reaction of Fe2O3 with aluminum powder. This is known as... View Article

With the help of a diagram explain the method of refining of copper by electrolysis.

A block of impure copper is taken as an anode or positive electrode. Copper sulfate which is acidified with sulphuric acid is used as a... View Article

Two ores X and Y were taken. On heating these ores it was observed that (a) ore X gives CO2 gas, and (b) ore Y gives SO2 gas. Write steps to convert these ores into metals, giving chemical equations of the reactions that take place.

(a) ore X gives CO2 gas, hence, it is a metal carbonate. Calcination- Metal carbonate heated strongly in the presence of limited supply of air it... View Article

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.

(a) Red colour is selected for danger signals because the red colour has a longer wavelength which makes it is the least scattered colour by fog... View Article

A student uses spectacles of focal length – 2·5 m. (a) Name the defect of vision he is suffering from. (b) Which lens is used for the correction of this defect? (c) List two main causes of developing this defect. (d) Compute the power of this lens.

A student uses spectacles of focal length −2.5m. (a) The, defect of vision he is suffering from is myopia or short-sightedness because the focal... View Article

(a) A coil of insulated wire is connected to a galvanometer. What would be observed if a strong bar magnet with its south pole towards one face of the coil is (i) moved quickly toward it? (ii) moved quickly away from it? (iii) held stationary near it? (b) Name the phenomena involved. (c) State the conclusion based on the observations in (i), (ii) and (iii).

(a) A coil of insulated wire is connected to a galvanometer and if a bar magnet with its south pole, towards one face of the coil, is (i) moved... View Article

Draw ray diagram in each of the following cases to show what happens after reflection to the incident ray when (a) it is parallel to the principal axis and falling on a convex mirror. (b) it is falling on a concave mirror while passing through its principal focus. (c) it is coming oblique to the principal axis and falling on the pole of a convex mirror.

(a) When the incident ray is parallel to the principal axis and falling on a convex mirror, then it gets diverged and appears to be coming from... View Article

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