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state principal of pin hole camera??

Pinhole cameras rely on the fact that light travels in straight lines – a principle called the rectilinear theory of light. This makes the image appear upside down in the camera. ... When the shutter is opened, light shines through to imprint an image on photographic paper or film placed at the back of the camera

Explanation:

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

grav forces affect all objects magnetic forces affect magnetic objects and electric currents