Electric Potential

The graph shows how the gravitational potential varies with distance between two planets, K and L, that have the same radius.

Which statement is correct?

• The mass of L is greater than the mass of K.

• The gravitational field strength at the surface of L is greater than that at the surface of K.

• The escape velocity from planet L is greater than that from planet K.

• More work must be done to move a mass of 1 kg from the surface of K to a distant point, than 1 kg from the surface of L.

The diagram shows equipotential lines near a group of asteroids. Which arrow shows the direction of the gravitational field at X?

• ↑

• ↓

• ←

• →

Planet N has a gravitational potential –V at its surface. Planet M has double the density and double the radius of planet N. Both planets are spherical and have uniform density.

What is the gravitational potential at the surface of planet M?

• –16V

• –8V

• –4V

• –0.2V

A conducting sphere holding a charge of +10 μC is placed centrally inside a second uncharged conducting sphere.

Which diagram shows the electric field lines for the system?

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• 
• 

Two parallel metal plates of separation a carry equal and opposite charges. Which graph best represents how the electric field strength E varies with the distance x in the space between the two plates?

• 
• 
• 
• 

An electron on the surface of the Earth is placed in an electric field of strength 5000 N C⁻¹. What is the ratio shown for the electron?

• 1.1 × 10⁻¹⁴

• 2.9 × 10⁻¹⁰

• 3.4 × 10⁹

• 9.0 × 10¹³

Two fixed parallel metal plates P and Q are at constant electrical potentials of +100 V and +70 V respectively. A proton travelling from P to Q experiences a force F due to the electric field between P and Q, and a change of potential energy of ΔE_p.

Which line, A to B, in the table gives the direction of F and the value of ΔE_p?

• Direction of F: towards P

  ΔE_p: +30 eV

• Direction of F: towards Q

  ΔE_p: +30 eV

• Direction of F: towards Q

  ΔE_p: -30 eV

• Direction of F: towards P

  ΔE_p: -30 eV

An electron moves through a distance of 0.10 m parallel to the field lines of a uniform electric field of strength 2.0 kN C^–1. What is the work done on the electron?

• zero

• 1.6 × 10^–17 J

• 3.2 × 10^–17 J

• 1.6 × 10^–21 J

A parallel-plate capacitor is fully charged and then disconnected from the power supply. A dielectric is then inserted between the plates. Which row correctly identifies the charge on the plates and the electric field strength between the plates?

• Charge: Stays the same

  Electric field strength: Increases

• Charge: Increases

  Electric field strength: Decreases

• Charge: Increases

  Electric field strength: Increases

• Charge: Stays the same

  Electric field strength: Decreases

An electron moving with constant speed enters a uniform electric field at right angles to the direction of the field. What is true about the force acting on the electron?

• It is at right angles to the direction of the field.

• It is in the opposite direction to the direction of the field.

• It causes the electron to continue in the same direction with its speed increasing steadily.

• It causes the electron to continue in the same direction with its speed decreasing steadily.