Magnetic Field due to Straight Wire & Right Hand Thumb Rule - UNSOLVED PRACTICE SET

Q7. Describe the shape and pattern of magnetic field lines around a long, straight, current-carrying conductor.

Q8. State the Right Hand Thumb Rule. How is it used to find the direction of the magnetic field around a straight current-carrying wire?

Q9. A current flows vertically upward through a straight wire. Using the Right Hand Thumb Rule, determine the direction of the magnetic field lines at a point to the East of the wire.

Q10. How does the magnetic field strength around a straight wire depend on
(a) the current, and
(b) the distance from the wire? State both relationships.

Q11. Why are the magnetic field lines around a straight wire drawn as concentric circles rather than straight lines or ellipses?

Q12. A student holds a compass below a vertical wire carrying current upward. The compass needle points East. If the current direction is reversed, what will the compass show? Explain using the Right Hand Thumb Rule.

Q13. Explain the magnetic field due to a straight current-carrying conductor in detail. Your answer must cover:
(a) the shape of the field lines (concentric circles) and why this shape arises,
(b) the Right Hand Thumb Rule and how to apply it with a clear example,
(c) how the field strength varies with distance from the wire (inverse relationship),
(d) how the field strength varies with current (direct relationship), and
(e) what happens to the field pattern if the wire is bent into different shapes (brief mention as a lead-in to circular loops).

Q14. A vertical current-carrying wire passes through the centre of a horizontal table. Four compasses are placed on the table at the North, South, East, and West positions around the wire, equidistant from it.
(a) If the current flows upward through the wire, use the Right Hand Thumb Rule to determine and describe the direction each compass needle would point (in terms of deflection from North).
(b) Draw or describe the overall pattern formed by all four compasses.
(c) If the current is reversed (now flowing downward), how would each compass reading change?
(d) If the compasses are moved twice as far from the wire, how would the deflections change?

Q15. An electrician in a workshop wants to determine the direction of current flow in a hidden wire embedded in a wall, without cutting into the wall.
(a) Explain how he could use a small compass and the Right Hand Thumb Rule to determine the current direction (assuming he knows the wire's orientation).
(b) What precautions must be taken regarding the strength of the current and proximity of other magnetic materials? 

(c) Why might this method give unreliable results near large metal objects or other current-carrying wires?
(d) How is this principle used in real devices like current-sensing clamps (used by electricians)?

Q16. A long straight wire carries a current of 5 A vertically upward (out of the page, if viewed from above).
(a) Using the Right Hand Thumb Rule, describe the direction of the magnetic field at four points: directly North, South, East, and West of the wire (all in the horizontal plane).
(b) If the current is increased to 10 A, how does the magnetic field strength at a fixed point change?
(c) If a point P is twice as far from the wire as point Q, compare the magnetic field strengths at P and Q.

Q17. Two parallel straight wires, both carrying current in the SAME direction (say, both upward), are placed close to each other.
(a) Using the Right Hand Thumb Rule, sketch (or describe) the magnetic field pattern around each wire individually.
(b) In the region between the two wires, do the magnetic fields from each wire point in the same direction or opposite directions?
(c) What does this suggest about the force between the two wires (attractive or repulsive)? (You will study this force in detail in a later topic — just reason qualitatively here.)

Q18. A student wraps a single loop of wire around a pencil and connects it to a battery, creating current flow.
(a) At the topmost point of the loop, the current flows toward the East. Using the Right Hand Thumb Rule, find the direction of the magnetic field at the centre of the loop (directly below this point).
(b) Now consider the bottom-most point of the loop, where current flows toward the West (since it's a complete loop). Using the Right Hand Thumb Rule again, find the direction of the magnetic field at the centre due to this part.
(c) Do the fields from the top and bottom of the loop add up or cancel at the centre? What does this suggest about the field at the centre of a circular loop (which you'll study next)?