A circular annulus of inner radius r and outer radius R has a uniform charge density a. What will be the total charge on the annulus?
A. a*(R2-r2)
B. π*a*(R2-r2)
C. a*(R-r)
D. π*a* R2
Answer:B
A circular annulus of inner radius r and outer radius R has a uniform charge density a. What will be the total charge on the annulus?
A. a*(R2-r2) B. π*a*(R2-r2) C. a*(R-r) D. π*a* R2
Explanation: Total surface area of the annulus = π*(R2-r2) because it has outer radius R and inner radius r. We know surface charge density is the amount of charge stored on the unit surface area. In this case, surface charge density is a. Therefore total charge on the annulus = π*a*(R2-r2).