Answer:
A solenoid field is increased with the increase in the current flow through the coil.
Explanation:
A solenoid is a current carrying coil with a significant number of loops. It works like an electromagnet inside which, a uniform and strong magnetic field is created. The magnetic field outside the solenoid field is nearly zero but not exactly zero.
While experimenting with the solenoid, scientists came to know that the magnetic field generated by the solenoid increases with the increase in the current, flowing through the solenoid.
The magnetic field works strongly around the arena of coil. The field changes its direction only near the ends and gets weak. Else its uniform throughout the loops.
The magnetic field inside the solenoid can be formulated as,

Where,
B = Magnetic field generated by the solenoid
= Constant
I = Current flowing through the loops of the solenoid
The static frictional force is greater than the kinetic frictional force, so the static frictional force is greater than 1200 N.
<h2>
The secondary voltage is 115 V.</h2>
Explanation:
The primary to secondary voltage ratio is given as 4:1 .
That is

We need to find what is the secondary voltage if the primary voltage is 460 volts.
That is

Substituting in ratio equation

The secondary voltage is 115 V.
Answer:
Efficiency
Explanation:
- The amount of mechanical work an engine can do per unit of heat energy it uses is called its efficiency.
- It is also defined as the output divided by the total electrical power consumed.
- In terms of heat, efficiency of engine is given by :

are output heat and input heat respectively.
Hence, the correct option is (d) "efficiency"