Question

A current through a wire depends on time as i = α₀t + βt² where α₀ = 20 A/s and β = 8 As^-2. Find the charge crossed through a section of the wire in 15 s. 

a. 2100 C

b.11250 C

c. 2250 C

d. 260 C

Answer 1

Correct Answer is B) 11250 C 

Explaination :: 

 we have ,

 i = α₀t + βt²  , α = 20 A/s and β = 8As^-2 ,t = 15 sec  

We know that ,

\(i={ {dq\over dt}⇒ { \int_0^t idt}=\int_0^Q dq }\)

\(⇒ { \int_0^{15} (α_0t + βt^2)dt}={\int_0^Q dq }\) 

\(Q=[ { {α_0t ^2\over2}+{ βt^3\over 3}}]_0^{15}\) 

\(Q = 20×15×{15 \over 2 }+ 8×15×15×{15 \over3} – 0\) 

 Q = 11250 C