General Science GK Questions with Answers – Page 116

A normal umbilical cord contains two arteries and one vein, three blood vessels in all. The umbilical cord joins the developing foetus to the placenta.

The sensation of a sound persists in the human brain for roughly one tenth of a second, so a reflected sound must arrive at least that much after the original to be heard as a separate echo.

SONAR stands for Sound Navigation and Ranging. A transmitter on the ship sends short ultrasonic pulses into the water, the pulses are reflected from the sea bed, a submarine, an iceberg or a shoal of fish, and a detector records the returning echo.

Sound travels fastest in solids because their particles are packed closely and are strongly bound, so a disturbance is passed on to the next particle almost at once.

This is the band of frequencies to which a healthy human ear responds, and the upper limit falls with age.

A vacuum contains no particles, and a mechanical wave such as sound can travel only by making particles vibrate and hand the disturbance on to their neighbours.

In a sound wave the particles of the medium vibrate back and forth along the same line in which the wave is travelling, producing regions where they crowd together, called compressions, and regions where they spread apart, called rarefactions.

The flash and the clap are produced at the same instant by the same discharge.

Amplitude is the maximum displacement of a particle of the medium from its rest position, and the energy carried by a wave increases with the square of the amplitude.

Convert the units first: 1 kilohertz is 1000 hertz and 50 centimetres is 0.5 metre. The speed is frequency multiplied by wavelength, that is 1000 multiplied by 0.5, which gives 500 metres per second.

Pitch is the characteristic of a sound by which the brain judges it as shrill or flat, and it is decided by the frequency of the wave.

The speed of a wave is the product of its frequency and its wavelength, so the speed here is 50 hertz multiplied by 4 metres, that is 200 metres per second.

White light is a mixture of colours, and the refractive index of the glass of a prism is slightly different for each of them, being greatest for violet and least for red.

In myopia the eyeball is too long or the lens of the eye too strongly converging, so rays from a distant object meet in front of the retina and the person cannot see far objects clearly.

An optical fibre is a thin thread of glass or plastic with a core of higher refractive index surrounded by a cladding of lower refractive index.

On a hot day the air touching the road is heated and becomes rarer than the cooler air above it.

The power of a lens is the reciprocal of its focal length expressed in metres, that is P equals 1 divided by f. Fifty centimetres is 0.5 metre, and the reciprocal of 0.5 is 2, so the power is two dioptres.

A convex mirror curves outward and spreads the light that falls on it, so it always forms a virtual, erect and diminished image, whatever the distance of the object.

Rays reflected from a plane mirror diverge and only appear to come from a point behind the mirror, so the image cannot be caught on a screen and is virtual.

Newton passed a narrow beam of sunlight through a glass prism in a darkened room and obtained a band of seven colours on the wall, which he named the spectrum.