Answer:
Energy stored, U = 66.6 J
Step-by-step explanation:
It is given that,
Number of turns in the solenoid, n = 500
Radius of solenoid, r = 1.5 cm = 0.015 m
Distance, d = 15 cm = 0.15 m
Let U is the energy stored in the solenoid. Its formula is given by :
![U=(1)/(2)LI^2](https://img.qammunity.org/2020/formulas/physics/college/rryj32qwq4bq82nespv9e4kh1i25n6tjjv.png)
L is the self inductance of the solenoid
![L=\mu_o N^2A d](https://img.qammunity.org/2020/formulas/physics/college/t9ku17psr74jr0107mq5rxbunzjiuu27s5.png)
N is the no of turns per unit length
![L=\mu_o (n/d)^2A d](https://img.qammunity.org/2020/formulas/physics/college/yr9u50y0209fr3jj5982v89aq72jjqtmyf.png)
![L=(4\pi\cdot10^(-7)\cdot500^(2)\cdot\pi\cdot\left(0.015\right)^(2))/(0.15)](https://img.qammunity.org/2020/formulas/physics/college/ll4v0pqnxe61zl8l91chpnbtrcxo9gxchl.png)
L = 0.00148 Henry
![U=(1)/(2)* 0.00148* 300^2](https://img.qammunity.org/2020/formulas/physics/college/a5wc5oda1g7joiyy2rhmav56gslxj30e98.png)
U = 66.6 J
Out of given options, the correct option for the energy stored in the solenoid is 70 J. So, the correct option is (a) "70 J".