R.O.M quiz 1

Which of the following physical quantities does not have a value of zero on the surface of an isolated conductor?

• Electric potential at the surface

• Current flowing on the surface.

• Magnetic field near the surface.

• Electric field along the surface.

Three charges are located along the x axis as shown in the drawing. The mass of the –1.2 μC is 4.0 × 10^–9 kg. Determine the magnitude and direction of the acceleration of the –1.2 μC charge when it is allowed to move if the other two charges remain fixed.

• 2 × 10⁵ ms^-2, to the right

• 1 × 10⁵ ms^-2, to the left

• 7 × 10⁴ ms^-2, to the right

• 3 × 10⁵ ms^-2, to the left

A capacitor of capacitance 15µF is fully charged and the potential difference across its plate is 8.0 V. It is then connected into the circuit as shown. The switch S is closed at time t = 0. Which one of the following statements is correct?

• the time constant of the circuit is 6.0 ms.

• The initial charge on the capacitor is 12µC.

• After a time equal to twice the time constant, the charge remaining on the capacitor is Q_oe², where Q_o ts the charge at timen t=0.

• After a time equal to the time constant, the potential difference across the capacitor is 2.9 V.

The circuit diagram shows two capacitors of capacitances 300 μF and 500 μF connected in series with a 6.0 V battery. The charge in the 300 μF capacitor is

• 0.68 mC

• 1.8 mC

• 1.1 mC

• 4.8 mC

The principles of conservation of which two quantities are associated with Kirchhoff’s first and second laws?

• First Law : charge

  Second Law : energy

• First Law : charge

  Second Law : voltage

• First Law : energy

  Second Law : charge

• First Law : voltage

  Second Law : charge

A conducting loop of wire is placed in a magnetic field that is normal to the plane of the loop. Which one of the following actions will not result in an induced current in the loop?

• Rotate the loop about an axis that is parallel to the field and passes through the center of the loop.

• Increase the strength of the magnetic field.

• Decrease the area of the loop.

• Decrease the strength of the magnetic field.

The Hall effect cannot be used to measure

• the charge density

• the magnetic flux density

• the mass of charge carriers

• the type of charge carriers

A beam of positive ions travel through the velocity selector of a mass spectrometer. The electric field and magnetic field in the velocity selector are 60.0 kV m^-1 and 0.50 T respectively. What is the selected velocity?

• 3.0 x 10⁴ ms^-1

• 6.0 x 10⁴ ms^-1

• 1.2 x 10⁵ ms^-1

• 2.4 x 10⁵ ms^-1

Back e.m.f is induced in a spinning electric motor. Which statement about the back e.m.f is not true?

• It reduces the electric power supplied to the motor.

• Its magnitude is bigger when the motor starts to spin.

• Its direction is opposite to the direction of the voltage supplied.

• It is generated when an armature coil undergoes a magnetic flux change.

The energy stored in an inductor is in

• the electric field.

• the gravitational field.

• the electromagnetic field.

• the magnetic field.