Physics Worksheet With Answers - Terry Honan - Blinn College printable pdf download

Physics Worksheet With Answers - Terry Honan - Blinn College

Chapter B - Problems

Blinn College - Physics 2426 - Terry Honan

Problem B.1

A disk with a 12 cm radius is rotated through all possible orientations in a uniform electric field. If it is found that the maximum

electric flux is 300 N ÿ m

ë C then what is the magnitude of the electric field?

Solution to B.1

F = E × A = E A cos q ï F

= E A

max

300

max

ï E =

= 6630

p 0.12

Problem B.2

A flat surface of area A sits in an electric field of E = Xa, b, 0\. (This field is in the xy-plane.) What is the flux through the surface if

it sits

(a) in the yz-plane?

(b) in the xz-plane?

Solution to B.2

F = Ÿ E × „ A = E × A , where the first expression is the general definition of flux. This becomes the second form is the case of a

uniform field and a flat surface. For a flat surface we write A = A n

, where A is the area of the surface and n

is the unit normal

is a unit normal to a surface then so is -n

vector to the surface. If n

, giving a sign ambiguity in the flux.

Note that the dot product of a vector with a unit vector gives the component of the vector in the direction of the unit vector.

(a) n

= ± x

ï F = ± E

A = ± a A

= ± y

ï F = ± E

A = ± b A

(b) n

= ± z

ï F = ± E

A = 0

Physics Worksheet With Answers - Terry Honan - Blinn College