Download 2015 Q8 - Loreto Balbriggan

State Examination Commission – Physics Higher Level, 2015
Question 8
Define electric field strength.
(6)
Both Van de Graaff generators and gold leaf electroscopes are used to investigate static electricity in the laboratory.
Draw a labelled diagram of a gold leaf electroscope.
Describe how it can be given a negative charge by induction.
(20)
A Van de Graaff generator can be used to demonstrate point discharge.
Explain, with the aid of a labelled diagram, how point discharge occurs.
Describe an experiment to demonstrate point discharge.
(18)
The polished spherical dome of a Van de Graaff generator has a diameter of 40 cm and a charge of +3.8 μC.
What is the electric field strength at a point 4 cm from the surface of the dome?
(12)
____________________________________________________________
Define electric field strength.
(6)
Both Van de Graaff generators and gold leaf electroscopes are used to investigate static electricity in the laboratory.
Draw a labelled diagram of a gold leaf electroscope.
Describe how it can be given a negative charge by induction.
(20)
Textbook stuff
A Van de Graaff generator can be used to demonstrate point discharge.
Explain, with the aid of a labelled diagram, how point discharge occurs.
Describe an experiment to demonstrate point discharge.
(18)
Charges accumulate at points on metallic objects producing
intense electric fields which attract oppositely charged particles
(and repel like charges), created in the air by the field, towards
the point that eventually neutralise (discharge) the object.
Point discharge may be demonstrated by inserting a pivoted
pin wheel onto the top of a Van der Graaf generator and
charging it.
The pin wheel will start to turn as the ions in the air repel
the like charge at the point.
Alternatively, a candle flame will be seen to move if held to
the point.
The polished spherical dome of a Van de Graaff generator has a diameter of 40 cm and a charge of +3.8 μC.
What is the electric field strength at a point 4 cm from the surface of the dome?
−6
E =
q
3.8×10
5
−1
2 =
2 = 5.9×10 N C
−12
4 π ϵ0d
4 π×8.9×10 ×(0.24)
where d = distance from point to centre of dome = 24 cm = 0.24 m
C. Garvey 2015