Hall sensor is used to measure the following

 Explanation

 Hall Effect:

1. The Hall effect is the movement of charge carriers through a conductor towards a magnetic attraction. The phenomenon is named for Edwin Hall, who discovered the effect in 1879.
2. When a current-carrying conductor is placed in a perpendicular or transverse magnetic field, then at the edges of the conductor an emf is developed. This potential difference is called Hall emf and this phenomenon is called Hall Effect.
3. Hall emf is given as  \(% MathType!MTEF!2!1!+- % feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyramaaBa % aaleaacaWGibaabeaakiabg2da9iaadUeadaWgaaWcbaGaamisaaqa % baGcdaWcaaqaaiaadkeacaGGUaGaamyAaaqaaiaadshaaaaaaa!3E0D! {E_H} = {K_H}\frac{{B.i}}{t}\)

   Where,

   K_H = Hall Effect coefficient

    B = Magnetic flux density

    \(i\)= Current flowing through the conductor

     \(t\)= Conductor thickness in a transverse direction

4. When a current-carrying conductor is placed in a magnetic field, the (-ve) and (+ve) charge carriers get accumulated on both sides of the conductor. One can measure the emf produced by a voltmeter.

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Application of Hall Effect Sensors

1.Speed Detection

2.Proximity sensing (in Smartphones)

3.Current sensing application

4.Position Sensors (e.g., to measure the fuel level in the fuel tank in automobiles)

5.Spacecraft propulsion

6.Used as Magnetometers, to measure Magnetic field (compass used in Smartphones)

Option (d) is correct.