A circular loop of wire is rotated at constant angular speed about an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induce emf is zero? Explain a. any horizontal orientation will do
b. it must be vertical
c. it must make an angle 45 degrees to the vertical
d. none of these answers

Two large, flat, horizontally oriented plates are parallel to each other, a distance d apart. half way betwween the two plates the electric field has magnitude e. if the separation of the plates is reduced to d/2 what is the magnitude of the electric field half way between the plates?

Which describes an image that can be produced by a concave lens? the image is real and smaller than the object. the image is virtual and larger than the object. the image is virtual and smaller than the object. the image is real and larger than the object.

The frequency of vibrations of a vibrating violin string is given by f = 1 2l t ρ where l is the length of the string, t is its tension, and ρ is its linear density.† (a) find the rate of change of the frequency with respect to the following. (i) the length (when t and ρ are constant) (ii) the tension (when l and ρ are constant) (iii) the linear density (when l and t are constant) (b) the pitch of a note (how high or low the note sounds) is determined by the frequency f. (the higher the frequency, the higher the pitch.) use the signs of the derivatives in part (a) to determine what happens to the pitch of a note for the following. (i) when the effective length of a string is decreased by placing a finger on the string so a shorter portion of the string vibrates df dl 0 and l is ⇒ f is ⇒ (ii) when the tension is increased by turning a tuning peg df dt 0 and t is ⇒ f is ⇒ (iii) when the linear density is increased by switching to another string df dρ 0 and ρ is ⇒ f is ⇒