Define torque. Give its units.

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Jasmine Grover

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Torque is a measure of the ability of a force to rotate an object around an axis or a pivot. It is also known as the moment of force. Mathematically, torque (τ) is defined as the cross product of the force (F) and the distance (r) from the axis of rotation to the point of application of the force:

τ = r × F

where × denotes the vector cross product.

Torque

The units of torque depends on the units used for force and distance.

  • In the International System of Units (SI), the unit of force is the newton (N) and the unit of distance is the meter (m). Therefore, the unit of torque is the newton-meter (N⋅m).
  • In other systems of units, such as the British engineering system, the unit of force is the pound (lb) and the unit of distance is the foot (ft), so the unit of torque is the pound-foot (lb-ft).
  • The C.G.S unit of torque is dyne-cm.

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CBSE CLASS XII Related Questions

  • 1.
    The energy of an electron in an orbit in hydrogen atom is \( -3.4 \, \text{eV} \). Its angular momentum in the orbit will be:

      • \( \dfrac{3h}{2\pi} \)
      • \( \dfrac{2h}{\pi} \)
      • \( \dfrac{h}{\pi} \)
      • \( \dfrac{h}{2\pi} \)

    • 2.
      Four long straight thin wires are held vertically at the corners A, B, C and D of a square of side \( a \), kept on a table and carry equal current \( I \). The wire at A carries current in upward direction whereas the current in the remaining wires flows in downward direction. The net magnetic field at the centre of the square will have the magnitude:

        • \( \dfrac{\mu_0 I}{\pi a} \) and directed along OC
        • \( \dfrac{\mu_0 I}{\pi a \sqrt{2}} \) and directed along OD
        • \( \dfrac{\mu_0 I \sqrt{2}}{\pi a} \) and directed along OB
        • \( \dfrac{2\mu_0 I}{\pi a} \) and directed along OA

      • 3.
        Nuclides with the same number of neutrons are called:

          • Isobars
          • Isotones
          • Isotopes
          • Isomers

        • 4.
          A part of a wire carrying \( 2.0 \, \text{A} \) current and bent at \( 90^\circ \) at two points is placed in a region of uniform magnetic field \( \vec{B} = -0.50 \, \hat{k} \, \text{T} \), as shown in the figure. Calculate the magnitude of the net force acting on the wire.


            • 5.
              The magnetic field in a plane electromagnetic wave travelling in glass (\( n = 1.5 \)) is given by \[ B_y = (2 \times 10^{-7} \text{ T}) \sin(\alpha x + 1.5 \times 10^{11} t) \] where \( x \) is in metres and \( t \) is in seconds. The value of \( \alpha \) is:

                • \( 0.5 \times 10^3 \, \text{m}^{-1} \)
                • \( 6.0 \times 10^2 \, \text{m}^{-1} \)
                • \( 7.5 \times 10^2 \, \text{m}^{-1} \)
                • \( 1.5 \times 10^3 \, \text{m}^{-1} \)

              • 6.
                A ray of light MN is incident normally on the face corresponding with side AB of a prism with an isosceles right-angled triangular base ABC. Trace the path of the ray as it passes through the prism when the refractive index of the prism material is \( \sqrt{2} \), and \( \sqrt{3} \).

                  CBSE CLASS XII Previous Year Papers

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