Which of the following figures shows the correct magnetic field lines?

Overloading in an electric circuit causes fire. Many people are unaware of this fact. Amit, an intelligent student told people of his building about overloading. He told them various precautions to avoid it questions:

(i) What harm does overloading in the circuit cause?

(ii) What values are shown by Amit?

Raja had gone to his aunt’s home in a foreign country, where domestic electric supply is DC. An electrician working in her kitchen was trying to locate the electric wiring in a particular wall for some electrical work but failed to do so. Electrician, then suggested the breaking of substantial position of wall to Rajat’s aunt.

But Rajat told his aunt that he could locate the position of current carrying wires in the kitchen without any breakage. He brought a small device from market and within ten minutes, located the position of all current carrying wires on wall of his aunt got very happy from him.

Read the above passage and answer the following questions:

(i) Which device was purchased by Rajat?

(ii) What was noticed by Rajat when he moved this device slowly over the current carrying wires embedded kitchen?

(iii) What values are shown by Rajat in this episode?

If the key in the arrangement as shown below is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are

Three plotting compasses are to a solenoid carrying a current. How many of the compass needles will change direction, if the current through the solenoid is increased?

(Ignore the effect of the earth’s magnetic field).