Electricity 1

Static electricity, distibution of charge, electric fields,coulomb's Law

identify two hazards caused by static electricity

electric shock

point discharge

damage to electronic devices

static cling

how is charge distributed on a pear-shaped conductor

concentration of charge at pointed end

on the outer surface of the conductor

why is Coloumb’s law an example of an inverse square law

because the force is inversely proportional to the distance between the point charges squared

define electric field strength

the electric field strength at a point in an electric field is the force per unit positive charge at that point.

if a positively charged rod is brought near to a neutral conducting sphere. how can you charge the sphere negatively by induction

earth the sphere, remove the earth. then remove the charged rod

explain how point discharge occurs

at a sharp point there is a large accumulation of charge generating a field with large electric field strength that ionises the air around the point. Ions in the air are either strongly attracted or repelled from the point and move toward or away from it

state coloumb’s law of force between electric charges

the electrostatic force between two point charge is proportional to the product of their charges and inversely proportional to the square of the distance between them

give two differences between the gravitatonal force and the electrostatic force between two electrons

gravitational force is much smaller than the electrostatic force

gravitational forcce is always attractive but electrostatic force can be attractive or repulsive.

describe an experiment to show an electric field pattern

Apparatus- oil and semolina, large container,high voltaged.c. powe supply, metal plates,leads.

procedure- 1.set up apparatus as shown in diagram 2. sprinkle semolina on the oil between the plates 3. turn on the high voltage d.c. voltage

observation and conclusion- the semolina will form parallel lines between the plates showing the electric field pattern

electric field strength unit

newton per coloumb or volt per metre

describe an experiment to demonstrate that total charge resides on the outside of a conductor.

Apparatus- Van de graff genarator, metal can,gold leaf electroscope, proof plane

procedure- 1.set up apparatus charge metal can using the van de Graff generator. 2. touch the neutral plane against the inside of the can and test,using a gold leaf elctroscope, if it has become charged. 3. Repeat process to test the outside of the can

observation-the leaf on gold electroscope deflects for outside smaple only

conclusion- all the charges resides on outside of a hollow conductor

give an applicationf for charge residing on the outside surface of a conductor

electrostatic shielding, co-axial cable, Tv cable, to protect persons or equipment

draw a labelled diagram of an electroscope. why should the frame be earthed

the frame is earthed for safety reasons and also because the potential difference between leaves and frame determines degree of deflection of leaves

how does a full-body metal-foil suit protect an operator when working on high voltage power lines

the suit blocks out external electrical fields, acts as faradays law

what is an electric field

an electric field is any region of space where a static electric charge experiences a force other than the force of gravity

describe how a gold leaf electroscope can be given a negative charge by induction

bring a charged rod close to the cap of the GLE. Earth the cap. remove the earth. then remove the charged rod

describe an experiment to demonstrate point discharge

apparatus- Van de Graff generator, static spinner

procedure- attach the static spinner to the dome of the VAn de Graff generator

Observation- the arms of the spinner rotate

conclusion-an electric wind is blown away from the points of the arms due to the point discharge

describe a laboratory experiment to demonstrate charging by induction

apparatus- Hollow sphere on insulated stand, polythene and Perspex rods, cloth.

procedure- 1.charge the polythene rod by friction with cloth. 2. bring the charged rod close to the sphere. 3. earth the sphere by touching. 4. remove the earth, then remove the charged rod. 5. repeat procedure with the Perspex rod

Observation and conclusion- a gold leaf electroscope can be used to show that the polythene rod induces a negative charge on the sphere and the Perpex induces a positive charge on it