Dùng một gương phẳng G để hắt 1 chùm ánh sáng mặt trời hẹp xuống đáy một cái giếng cạn hình trụ thẳng đứng dọc theo trục của giếng. Tính góc hợp bởi mặt gương và đường thẳng đứng, biết rằng các tia sáng mặt trời nghiêng với mặt phẳng nằm ngang một góc 60°C

Search coils and credit cards. one practical way to measure magnetic field strength uses a small, closely wound coil called a search coil. the coil is initially held with its plane perpendicular to a magnetic field. the coil is then either quickly rotated a quarter-turn about a diameter or quickly pulled out of the field. (a) derive the equation relating the total charge q that flows through a search coil to the magnetic-field magnitude b. the search coil has n turns, each with area a, and the flux through the coil is decreased from its initial maximum value to zero in a time ∆t. the resistance of the coil is r, and the total charge is q = i∆t, where i is the average current induced by the change in flux. (b) in a credit card reader, the magnetic strip on the back of a credit card is rapidly “swiped” past a coil within the reader. explain, using the same ideas that underlie the operation of a search coil, how the reader can decode the information stored in the pattern of magnetization on the strip. (c) is it necessary that the credit card be “swiped” through the reader at exactly the right speed? why or why not?

Acoil suspended freely, points in some direction when no current is passed through it . can you tell what will happen when a current is passed though it?

Apiece of metal 75g at 110°c is dropped in a container with 500g at 20°c. the h2o if temperature is 24°c find specific heat capacity of metal