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Choose the best option about lightning:

Lightning occurs as a result of the flow of charge from clouds to the ground i.e. It happens through the process of electric discharge between... View Article

How to calculate the energy of a photon?

The energy of a photon is calculated in two ways as follows: If the frequency f of the photon is known, then we use the formula E = hf.This... View Article

A particle which has zero rest mass and non-zero energy and momentum must travel with a speed

Particle is photon and it travels with the velocity equal to light in vacuum m0 = 0 ∴ v = c... View Article

Which of the following decreases in motion along a straight line with constant retardation while the body is moving away from the origin?

When a body moves along a straight line with constant retardation, its speed goes on decreasing in moving away along a straight line.... View Article

In Millikan’s experiment for thedetermination of the charge on the electron, the reason for using the oil is

In Millikan's experiment, drops of non-volatile liquid (cloak oil) are used to prevent evaporation. ... View Article

Due to internal combustion inside a rocket, gases are ejected at the rate of 2.4 kg/minute. The velocity of the gases with respect to the rocket is 400 m/s. Calculate force exerted on the rocket

Rate of change of mass = (dm/dt) = 2.4kg/minute = (2.4/60) kg/sec = 0.04 kg/secForce= Rate of change of momentum =v(dm/dt) + m(dv/dt). =... View Article

What do you see if you look at the clouds closely with electroscope ? 1. Upper parts of the clouds are positively charged. 2. Cloud is electrically neutral (no charge) everywhere. 3. Upper parts of clouds are negatively charged. 4. Lower parts of clouds are negatively charged.

In clouds, the upper parts are usually positively charged and the lower parts are usually negatively charged.... View Article

The coordination number of Cu is [AMU 1992]

Cu has fcc structure, for fccstructure co-ordination number = 12... View Article

When 2 charged glass rods, after being rubbed with silk cloths, are brought towards each other, they

Glass rods acquire positive charges. When these rods possessing like charges are brought towards each other, they repel each other.... View Article

A bullet of mass 0.02 kg is fired from a rifle. The bullet takes 0.02s to move through the barrel and leaves with a velocity of 200 ms–1. What is the acceleration acting on the bullet?

Initial velocity of the bullet = 0 ms-1Final velocity of the bullet = 200 ms-1 Time to travel = 0.02 s Using v= u + at a= (v-u)/t =... View Article

In anamplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be [AMU 1996]

Carrier frequency > audio frequency ... View Article

The charge which is acquired by the glass rod when rubbed with a piece of silk is?

It is a convention to consider the charge acquired by a glass rod when it is rubbed with silk as positive.... View Article

Statement 1: The flow of current in a poor conductor is impossible. Statement 2: Under certain conditions current flows through a poor conductor.

Poor conductors are those, which do not allow electricity to flow through them easily, but under certain conditions we can make current flow... View Article

Which one of the series of hydrogen spectrum is in the visible region [RPMT1999;MP PET 1990; MP PMT 1994;AFMC 1998; CBSE PMT 1990; MH CET 2004]

Balmer series lies in the visible region... View Article

Image is formed for the short sighted personat [AFMC 1988]

In short sightedness, the focal length of eye lens decreases, so image is formed before retina.... View Article

Statement 1: Poor conductors do not allow electric current to flow through them. Statement 2: Poor conductors do not allow electric current to flow through them easily.

Poor conductors do not allow electric current to flow through them easily, but under certain conditions they may conduct electricity.... View Article

Like sound light also cannot travel in vacuum.

Light can travel in vaccum but sound cannot. ... View Article

There is a sample of water. However it is not known if it is pure distilled water or contains salts and other impurities. Can you determine if it will conduct electricity or not with just the given information?

Pure water is not a conductor of electricity. But the presence of salts, minerals etc makes it a conductor.... View Article

Why does the needle of a magnetic compass deflect when it is kept beside a current carrying wire?

A current carrying wire always produces a magnetic field around it and due to this magnetic field the needle of magnetic compass deflects. ... View Article

Statement 1: It is observed that sometimes a bulb glows brighter and sometimes it glows dim. Statement 2: Glowing brighter and dimmer depends on heating effect of current. More current produces more heating effect making the bulb glow brighter and vice-versa.

More current produces more heating effect and hence the filament heats up completely and it glows brighter but it glows dimmer when less current... View Article

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