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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?

Which two statements are true about a system? a system is a group of objects analyzed as one unit. energy that moves across system boundaries is conserved there's only one way to define the boundaries of a system all systems are made by humans

Aball is fired with an initial velocity of 500 m/s at an angle of 30 degrees above the horizontal across a level field. a. what are the horizontal and vertical components of the initial velocity. b. calculate the maximum height, the time of flight, and the range of the ball.