Answer:
A.The spring constant for B is one quarter of the spring constant for A.
Explanation:
If spring A oscillates at twice the frequency of spring B, and period is frequency inverted. It means spring B has a period twice of spring A's.

As
, and the 2 springs have the same mass




So A.The spring constant for B is one quarter of the spring constant for A. is the correct answer.
Answer:
(a) Energy density will be equal to 
(b) Total energy will be equal to 0.0718 J
Explanation:
It is given that length of solenoid l = 78.8 cm = 0.788 m
Cross sectional area 
Number of turns of the wire N = 914
Current in the solenoid i = 8.25 A
Inductance of the wire is equal to 
(b) Total energy stored in magnetic field 
(a) Energy density will be equal to

The core has positive charge<span>, the electrons have negative </span>charge. When you are rubbing<span> the </span>glass rod<span> with the </span>silk cloth<span>, electrons are stripped away from the atoms in the </span>glass<span> and transferred to the </span>silk cloth<span>. This leaves the </span>glass rod<span> with more </span>positive<span> than negative </span>charge<span>, so you get a net </span>positive charge<span>.</span>