An air heater may be fabricated by coiling nichrome wire and passing air in cross flow over the wire. consider a heater fabricated from wire of diameter d = 2.0 mm, electrical resistivity rho_e = 10^6 ohm middot m, thermal conductivity k = 25 w/m middot k, and emissivity epsilon = 0.2. the heater is designed to deliver air at a temperature of t_infinity = 70.5 degree c under flow conditions that provide a convection coefficient of h = 261 w/m^2 middot k for the wire. the temperature of the housing that encloses the wire and through which the air flows is t_sur = 70.5 degree c.
(a) if the maximum allowable temperature of the wire is t_max = 1200 degree c, what is the maximum allowable electric current i? if the maximum available voltage is delta e = 193 v, what is
(b) the corresponding length l of wire that may be used in the heater and
(c) the power rating of the heater?
(a) i_max = a
(b) l = m
(c) p_elec = kw

Anne applies a force on a toy car and makes it move forward. what can be said about the forces acting on the toy car at the moment anne applies the force?

Física: un futbolista patea hacia el arco con una velocidad de 15m/ah, calcular: a)el alcance para un ángulo de tiro de 25? , b) el tiempo que el balón permanece en el aire.

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?