General Science GK Questions with Answers – Page 12

Thomas Young passed light from one source through two narrow slits placed close together and obtained alternate bright and dark bands on a screen.

Polarisation means restricting the vibrations of a wave to one plane, which is only possible if the vibrations are perpendicular to the direction of travel.

The smallest angular separation a telescope can resolve is 1.22 times the wavelength divided by the diameter of the objective, so a larger aperture means a smaller limit of resolution and a greater resolving power.

Diffraction, the bending of a wave round an edge, is appreciable only when the obstacle or opening is of the same order of size as the wavelength.

By Malus's law the intensity transmitted by the second Polaroid is the intensity falling on it multiplied by the square of the cosine of the angle between the two transmission planes.

The fringe width equals the wavelength multiplied by the distance of the screen and divided by the separation of the two slits.

The light reflected from the upper surface of the thin film and the light reflected from the lower surface travel slightly different distances and interfere.

Only a transverse wave, in which the vibrations are at right angles to the direction of travel, can have those vibrations restricted to a single plane by a Polaroid.

Inserting a plate of thickness t in one arm makes the light cross it twice, so the extra path introduced is twice the thickness times the quantity refractive index minus one.

By the Rayleigh criterion the smallest angle the eye can resolve is 1.22 times the wavelength divided by the diameter of the pupil, that is 1.22 multiplied by 500 nanometres and divided by 3 millimetres, which comes to about 2.03 times ten to the power minus four radian.

Brewster found that when unpolarised light falls on a transparent surface at one particular angle of incidence, called the polarising angle, the reflected light is completely plane polarised, and at that angle the refractive index of the surface equals the tangent of the polarising angle.

If the frequency of the soldiers' rhythmic steps happens to match the natural frequency of the bridge, the bridge is driven at its own frequency and its amplitude of vibration can build up to a dangerous level; breaking step destroys the rhythm and avoids the risk.

The Dutch scientist Huygens designed the first working pendulum clock in 1656, after Galileo had noticed that a swinging lamp took the same time for each swing whether it swung far or little, the property called isochronism.

In simple harmonic motion the acceleration equals minus omega squared times the displacement, so it grows with displacement and is greatest at the ends of the path, where its value is A omega squared and it points back towards the centre.

Potential energy is proportional to the square of the displacement, so it is greatest where the displacement is greatest, that is at the two ends of the path, where the body is momentarily at rest and its kinetic energy is zero.

The time period varies inversely as the square root of g, so if g falls to one sixth, the period is multiplied by the square root of six, about 2.45 times; the pendulum swings more slowly and a pendulum clock taken to the moon would lose time badly.

The time period varies as the square root of the length, so multiplying the length by four multiplies the period by the square root of four, that is by two; to double the period of a pendulum its length must be made four times.

A second's pendulum is one whose time period is exactly two seconds, so that each swing from one side to the other takes one second.

The time period of a simple pendulum is two pi times the square root of the length divided by g, in which the mass of the bob does not appear at all; a heavy bob and a light bob of the same length keep the same time, which is the…

A swing is a pendulum, and its speed is greatest at the lowest point, where all the potential energy gained at the top has turned into kinetic energy.