The presence of magnetic field can be determined using which one of the following instruments?

The presence and direction of a magnetic field can be determined using a magnetic needle, commonly known as a compass [1][5]. A magnetic field is a region surrounding a magnet or a current-carrying wire where magnetic forces can be detected [1]. When a magnetic needle is placed within this field, it experiences a torque that causes it to rotate and align with the magnetic field lines [2][5]. The deflection of the needle indicates the presence of the field, while the direction in which the north pole points indicates the field's orientation [2][3]. While ammeters and voltmeters are used to measure electric current and potential difference respectively, they often utilize magnetic effects internally but are not the primary instruments for detecting the field itself. A magnetic needle remains the fundamental tool for mapping and identifying the existence of magnetic fields [5].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > What you have learnt > p. 206
2. [5] https://satheejee.iitk.ac.in/article/physics/physics-ammeter/
3. [2] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > Activity 12.3 > p. 197
4. [3] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > Activity 12.5 > p. 199