The line joining places where the magnetic declination is zero is called the:
- A.Isogonic line
- B.Agonic line
- C.Isoclinic line
- D.Aclinic line
Correct answer
Explanation
The correct answer is B, the agonic line. Magnetic declination is the angle between true north and magnetic north, and along the agonic line that angle is zero, so a compass needle there points to true north. Option A is wrong because an isogonic line joins places having the same declination, of whatever value; the agonic line is simply the particular isogonic line for zero. Option C is wrong because an isoclinic line joins places having the same magnetic dip or inclination, the angle the needle makes with the horizontal. Option D is wrong, though it is the closest trap: the aclinic line is the line of zero dip, that is the magnetic equator, where a freely suspended needle stays horizontal. Declination gives agonic, dip gives aclinic.
Read the full article: Geographical Terms and Isolines: Isobar to Isohyet
Practice Questions
View allLines drawn on a map joining places that receive equal amounts of rainfall are called:
- A.Isobars
- B.Isohyets
- C.Isohels
- D.Isotherms
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The word comes from the Greek hyetos, meaning rain, so an isohyet joins all places on a map that receive the same amount of rainfall in a given period; rainfall distribution maps of India, which show the 200 centimetre and 50 centimetre lines, are drawn with isohyets.
Read the full explanation →An isohel is a line on a map joining places having equal:
- A.Cloudiness
- B.Duration of sunshine
- C.Humidity
- D.Salinity
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An isohel, from the Greek helios for the sun, joins places that receive sunshine for an equal number of hours, and such maps are used in studies of solar energy potential and of crop seasons.
Read the full explanation →Lines joining points of equal depth of water in an ocean or a lake are known as:
- A.Isobars
- B.Isobaths
- C.Isopachs
- D.Isohypses
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The Greek bathos means depth, so isobaths are the depth contours of a bathymetric chart; the 200 metre isobath is conventionally taken as the outer edge of the continental shelf.
Read the full explanation →Isoseismal lines on a map are drawn to show equal:
- A.Intensity of an earthquake
- B.Thickness of rock strata
- C.Travel time from a place
- D.Wind speed
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Isoseismal lines join points at which the shaking of an earthquake was felt with the same intensity, and because intensity falls away from the source, they are drawn as roughly concentric closed curves around the epicentre, the point of the surface vertically above the focus.
Read the full explanation →A narrow strip of land that joins two larger landmasses and separates two seas is called:
- A.A strait
- B.An isthmus
- C.An archipelago
- D.A peninsula
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The Isthmus of Panama joins North and South America and separates the Caribbean Sea from the Pacific, and the Isthmus of Suez joins Africa to Asia; both have been cut by canals precisely because they are narrow.
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