It causes or makes a magnetic field.
(a) The distance of the image formed by the concave mirror is 19.1 cm.
(b) The image formed is diminished and real.
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Image distance </h3>
The distance of the image formed by the concave mirror is calculated as follows;
1/f = 1/v + 1/u
1/v = 1/f - 1/u
1/v = 1/15 - 1/70
1/v = 0.05238
v = 1/0.05238
v = 19.1 cm
The image distance is smaller than object distance, thus the image formed is diminished and real.
Learn more about concave mirror here: brainly.com/question/13164847
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The middle or centre of the Earth is the core. However the middle of the layers from the surface to the centre of the Earth is known as mantle.