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Physics > Electricity 1 > Flashcards

Electricity 1 Flashcards

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1
Q

Why is a lightning conductor made of copper?

A

Copper is a good electrical conductor.

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2
Q

What is meant by electric field strength?

A

Force per unit charge

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3
Q

Why do the ions near the lightning conductor accelerate?

A

Near the lightning conductor there is a large value of electric field strength which exerts a large force on the ions causing them to accelerate.

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4
Q

How does the presence of ions in the air cause the air to be more conducting?

A

The ions act as charge carriers.

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5
Q

How do charged clouds become neutralised?

A

Charge from the cloud flows through the ionized air to the lightening conductor, to the earth.

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6
Q

Why are raised umbrellas and golf clubs not recommended during thunderstorms?

A

They could act as lightning conductors, i.e a large charge could flow through them. A person in contact with them would conduct some of this charge and be electrocuted.

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7
Q

Explain why pointed surfaces should be avoided when using high voltage electrical equipment.

A

Point discharge may occur. This flow of charge through air could lead to a spark, causing a fire.

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8
Q

Define electric field strength and give it’s unit.

A

E = F/q unit = NC-1

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9
Q

How would you demonstrate an electric field pattern?

A
  • Place two aluminium electrodes in a beaker of olive oil. The voltage across the electrodes would be of order of 2000 V.
  • Sprinkle semolina grains on the oil.
  • The grains line up in such a way that they show the electric field pattern.
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10
Q

Define potential difference.

A

P.t between 2 points is the work done per unit charge in moving the unit from one point to another.

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11
Q

Define capacitance

A

C = q/V

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12
Q

Describe what happens in the circuit when the 6 V d.c. supply is replaced with a 6 V a.c. supply.

A

The current continually flows up to and back from the capacitor i.e the capacitor is charged and dischared.

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13
Q

Describe what happens in the circuit when the 6 V d.c. supply is replaced with a 6 V a.c. supply.

A

The current continually flows up to and back from the capacitor i.e the capacitor is charged and discharged.

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14
Q

Define electric field strength.

A

E = F/q

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15
Q

State Coulomb’s law an example of an inverse square law?

A

F = Q1 x Q2 / 4 π e d²

Why: Since F

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16
Q

Give two difference between the gravitational force and the electostatic force between two electrons.

A
  • Gf is attractive and electrostatic is repulsive

- Gf is much smaller than the electrostatic force

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17
Q

List the factors that affect the capacitance of a parallel plate capacitor.

A
  • Common area of the plates
  • Distance between the plates
  • Permittivity of the medium between the plates
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18
Q

What is the net charge on the capacitor?

A

Zero (plates have equal and opposite charges)

19
Q

Give a use for a capacitor

A
  • Tuning a radio from one station to another

- A smoothing unit when converting a.c. to d.c.

20
Q

Define electric field strength and give its unit of measurement.

A

E = F/q unit - NC-1

21
Q

Define electric field strength and give its unit of measurement.

A
  • E = F/q

- unit - NC-1

22
Q

Describe how an electric field pattern may be demonstrated in the laboratory

A
  • Place two aluminium electrodes in a beaker of olive oil. The voltage across the electrodes would be of order of 2000 V.
  • Sprinkle semolina grains on the oil.
  • The grains line up in such a way that they show the electric field pattern.
23
Q

All the charge resides on the surfaces of a Van de Graff generator’s dome. Explain why.

A

The like charges on the dome repel each other and move to be at the maximum distance away from each other, i.e on the surface.

24
Q

Give an application that the total charge resides on the outside of a conductor.

A
  • Co-axial cable
  • Electrostatic shielding
  • Faraday cage
25
Q

Define capacitance

A

C = Q/V

26
Q

Describe how an electroscope can be charged by induction.

A
  • Bring a positively charged rod near the cap of the electroscope. The gold leaf rises. The leaf region is positively charged. The cap has a negative charge.
  • Touch the cap with your finger (earth the cap). The leaf falls as the charge in that region is neutralised. Electrons come from the earth to the leaf region to neutralise the positive charges.
  • Remove your finger from the cap. Then remove the positively charged rod. The leaf rises again as the negative charge from the cap spreads over the leaf region and the cap.
27
Q

Define potential difference.

A

The potential difference between A and B is the work done per unit charge to move a charge from B to A.

28
Q

Define capacitance.

A

C = q/V

29
Q

Describe an experiment to demonstrate that a capacitance stores energy.

A
  • When the switch is closed the capacitor is charged up from the battery.
  • You now open the switch and replace the battery with a bulb.
  • You now close the switch and the bulb lights briefly.
  • The conclusion is that the charged capacitor stored energy.
30
Q

Define electric field strength and give its unit of measurement.

A

E = F/q

31
Q

Under what circumstances will point discharge occur?

A

Will occur when there is a high concentration of charge at a sharp point.

32
Q

State Coulomb’s law

A

The force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them.
F ∝ q1q2 / d²

33
Q

Define the unit of charge, the coulomb.

A

The charge that passes a point when a current of 1 amp flows for 1 second.

34
Q

Define electric field.

A

The region around as charged object in which its electric forces act.

35
Q

Describe an experiment to demonstrate an electric field pattern.

A
  • Place two aluminium electrodes in a beaker of olive oil. The voltage across the electrodes would be of order of 2000 V.
  • Sprinkle semolina grains on the oil.
  • The grains line up in such a way that they show the electric field pattern.
36
Q

State two differences between a capacitor or a battery.

A
  • Capacitors store electrical energy while batteries store chemical energy.
  • Capacitors discharge faster than batteries.
  • Batteries give a constant current while capacitors do not.
37
Q

What is meant by polarisation of light?

A

The process of confining the vibrations of the light wave to one direction (plane).

38
Q

Give two applications of capacitors, other than in touchscreens.

A
  • Tuning a radio from one station to another

- A smoothing unit when converting a.c. to d.c.

39
Q

Draw a labelled diagram of a gold leaf electroscope.

A

x

40
Q

Describe how a gold leaf electroscope can be give a negative charge by induction.

A
  • Bring a positively charged rod near the cap of the electroscope. The gold leaf rises. The leaf region is positively charged. The cap has a negative charge.
  • Touch the cap with your finger (earth the cap). The leaf falls as the charge in that region is neutralised. Electrons come from the earth to the leaf region to neutralise the positive charges.
  • Remove your finger from the cap. Then remove the positively charged rod. The leaf rises again as the negative charge from the cap spreads over the leaf region and the cap.
41
Q

State the unit of capacitance.

A

Farad

42
Q

What is the net charge of the capacitor when it stores energy?

A

ZERO!

43
Q

State the unit of potential difference.

A

Volt

44
Q

Explain how point discharge occurs.

A
  • Charge accumulates at the sharp point on the conductor . Air molecules near the sharp point of a charged object are ionised. The air molecules split into positive and negative ions.
  • The negative ions are attracted to the large concentration of positive ions at the sharp point. The negative ions combine with and neutralise some of the charge on the sharp point.
  • The positive ions are repelled by the very large concentration of positive ions at the sharp point. This movement of positive ions away from the sharp point gives rise to an electrostatic wind.

Physics (12 decks)

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