The roads near many traffi c lights contain buried sensors that detect when a car is present (waiting at a stop light). These sensors are large loops of wire just beneath the surface of the road.
(a) Explain how they can use the induced emf described by Faraday’s law to detect the presence of a car. Cars contain a lot of steel, which is magnetic.
(b) Explain why these sensors sometimes fail to detect a motorcycle and always fail to detect bicycles.