Match the items in List-$I$ with the items in List-$II$:
| List-$I$ | List-$II$ |
| :--- | :--- |
| $(A)$ High retentivity | $(i)$ Telephone diaphragm |
| $(B)$ High resistivity | (ii) Diamagnet |
| $(C)$ Low coercivity | (iii) To decrease eddy current losses |
| $(D)$ Negative susceptibility | (iv) Permanent magnet |

Demagnetisation of magnets can be done by

Write the differences between electrostatics and magnetics.

$(a)$ What happens if a bar magnet is cut into two pieces: $(i)$ transverse to its length,$(ii)$ along its length?
$(b)$ $A$ magnetised needle in a uniform magnetic field experiences a torque but no net force. An iron nail near a bar magnet,however,experiences a force of attraction in addition to a torque. Why?
$(c)$ Must every magnetic configuration have a north pole and a south pole? What about the field due to a toroid?
$(d)$ Two identical-looking iron bars $A$ and $B$ are given,one of which is definitely known to be magnetised. (We do not know which one.) How would one ascertain whether or not both are magnetised? If only one is magnetised,how does one ascertain which one? [Use nothing else but the bars $A$ and $B$.]

Two identical bar magnets are fixed with their centres at a distance $d$ apart. $A$ stationary charge $Q$ is placed at $P$ in between the gap of the two magnets at a distance $D$ from the center $O$ as shown in the figure.

Two short magnets of magnetic moment $1000 \, A m^2$ are placed as shown at the corners of a square of side $10 \, cm$. The net magnetic induction at $P$ is....$T$