Q. No.An electric dipole is placed at an angle of \(30^\circ\) with an electric field intensity \(2\times10^5~ \text{N/C}\). It experiences a torque equal to \(4~\text{N-m}\). The charge on the dipole, if the dipole length is \(2~ \text{cm}\), is:
1.
\(8~\text{mC}\)
2.
\(2~\text{mC}\)
3.
\(5~\text{mC}\)
4.
\(7~\mu \text{C}\)
An electron falls from rest through a vertical distance \(h\) in a uniform and vertically upward-directed electric field \(E\). The direction of the electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest through the same vertical distance \(h\). The fall time of the electron in comparison to the fall time of the proton is:
| 1. | smaller | 2. | \(5\) times greater |
| 3. | \(10\) times greater | 4. | equal |
A toy car with charge \(q\) moves on a frictionless horizontal plane surface under the influence of a uniform electric field \(\vec {E}.\) Due to the force \(q\vec {E},\) its velocity increases from \(0\) to \(6~\text{m/s}\) in a one-second duration. At that instant, the direction of the field is reversed. The car continues to move for two more seconds under the influence of this field. The average velocity and the average speed of the toy car between \(0\) to \(3\) seconds are respectively:
1. \(2~\text{m/s}, ~4~\text{m/s}\)
2. \(1~\text{m/s}, ~3~\text{m/s}\)
3. \(1~\text{m/s}, ~3.5~\text{m/s}\)
4. \(1.5~\text{m/s},~ 3~\text{m/s}\)
1. \(v\propto x\)
2. \(v\propto x^{-1/2}\)
3. \(v\propto x^{-1}\)
4. \(v\propto x^{1/2}\)
1. \(\frac{r}{\sqrt[3]{2}}\)
2. \(\frac{r}{\sqrt[2]{2}}\)
3. \(\frac{2r}{3}\)
4. none of the above
| 1. | be reduced to half |
| 2. | remain the same |
| 3. | be doubled |
| 4. | increase four times |
1. \(8\times 10^{7}\)
A thin conducting ring of the radius \(R\) is given a charge \(+Q.\) The electric field at the centre \(O\) of the ring due to the charge on the part \(AKB\) of the ring is \(E.\) The electric field at the centre due to the charge on the part \(ACDB\) of the ring is:
| 1. | \(3E\) along \(KO\) |
| 2. | \(E\) along \(OK\) |
| 3. | \(E\) along \(KO\) |
| 4. | \(3E\) along \(OK\) |
Three-point charges \(+q\), \(-2q\) and \(+q\) are placed at points \((x=0,y=a,z=0)\), \((x=0, y=0,z=0)\) and \((x=a, y=0, z=0)\), respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are:
| 1. | \(\sqrt{2}qa\) along \(+y\) direction |
| 2. | \(\sqrt{2}qa\) along the line joining points \((x=0,y=0,z=0)\) and \((x=a,y=a,z=0)\) |
| 3. | \(qa\) along the line joining points \((x=0,y=0,z=0)\) and \((x=a,y=a,z=0)\) |
| 4. | \(\sqrt{2}qa\) along \(+x\) direction |
A hollow cylinder has a charge \(q\) coulomb within it (at the geometrical centre). If \(\phi\) is the electric flux in units of Volt-meter associated with the curved surface \(B,\) the flux linked with the plane surface \(A\) in units of volt-meter will be:
1. \(\frac{1}{2}\left(\frac{q}{\varepsilon_0}-\phi\right)\)
2. \(\frac{q}{2\varepsilon_0}\)
3. \(\frac{\phi}{3}\)
4. \(\frac{q}{\varepsilon_0}-\phi\)
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