Typical of Question 5 in Leaving Cert. Exam Q1 Answer all of the following parts (a), (b), (c), etc.
(a) How do you charge a Perspex rod? What type of charge will it typically hold? (7)
(b) Give one difference between the structure of a good conductor and a good insulator. (7)
(c) State two factors affecting the amount of static charge that can build up on the dome of a Van de Graaff generator. (7)
(d) A pear-shaped conductor is placed on an insulated stand as shown in Fig 15.22. The conductor is given a negative charge. Copy the diagram and show how the charge is distributed over the conductor.
Fig 15.22
(e) Give two differences between Newton’s law of gravitation and Coulomb’s law of electrostatic force. (f) Draw the pattern of an electric field around two positive point charges placed close to each other. (g) Identify two positive applications of static electricity.
(h) Calculate the size of the electrostatic force between two electrons that are 1 104 m apart. The charge on an electron is 1.6 1019 C, permittivity of free space 8.9 1012 F m1.
(i) The permittivity of Pyrex is 4.183 1011 F m1. Calculate its relative permittivity. The permittivity of free space 8.9 1012 F m1.
E
(j) What is the force exerted on an electron when it is in an electric field of strength 8 N C1? The charge on an electron is 1.6 1019 C.
(7) (7)
(7) (7) (7) (7)
‘SECTION B’
FULL QUESTION Q2 Describe how an electric field pattern may be demonstrated in the laboratory.
Define electric field strength and give its unit of measurement. A spherical conductor of external diameter of 20 cm has a positive charge of 2 C on it.
(i) What is the electric field strength at a point 10 cm from the sphere? Permittivity of free space 8.9 1012 F m1.
(ii) What is the electrostatic force exerted on the 3 C point charge at this distance?
(iii) What would the effect be on the force on the point charge were it to be placed 30 cm away from the surface of the sphere rather than 10 cm away?
State Coulomb’s law of force between electric charges. How are integrated circuits protected from sparks due to strong electric fields?
