The magnetic field produced by a current-carrying solenoid depends directly upon the strength of the current.

$(a)$ Describe an activity to determine the direction of magnetic field produced by a current-carrying straight conductor. Also,show that the direction of the magnetic field is reversed on reversing the direction of current.
$(b)$ An $\alpha$-particle (which is a positively charged particle) enters a uniform magnetic field at right angles to it as shown below. Stating the relevant principle,explain in which direction will this $\alpha$-particle move?

You are given two identical-looking iron bars,out of which one of them is a magnet. Just using these two bars,how will you identify which one is a magnet?

$(a)$ Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another.
$(b)$ List any two properties of magnetic field lines.

In the below figure,$A$ and $B$ represent two straight wires carrying equal currents in a direction at right angles to the plane of paper inwards. Sketch separately the magnetic field lines produced by each current. Give a reason why the magnetic field at $K$ (mid-point of the line joining $A$ and $B$) will be zero.
What will be the effect on the magnetic field at $K$ if the current in wire $B$ is reversed?

Draw the pattern of magnetic field lines through and around a current-carrying circular loop of wire. How would the strength of the magnetic field produced at the centre of the circular loop be affected if: $(i)$ the strength of the current passing through this loop is doubled? $(ii)$ the radius of the loop is reduced to half of the original radius?