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LAET A-level OCR Physics A 2023 > Capacitors and Electric Fields > Flashcards

Capacitors and Electric Fields Flashcards

1
Q

Define the electric field strength

A

The force per unit charge on a positive test charge placed at that point

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2
Q

Define capacitance

A

charge per unit potential difference

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3
Q

What is the Farad?

A

coulomb per volt

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4
Q

Define the Electric Potential

A

Work done per unit charge to bring a positive charge from infinity to that point in the field

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5
Q

Define the Electric Potential Energy

A

Work done to bring a small positive charge from infinity to that point in the field

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6
Q

What is the time constant of a circuit containing a capacitorand a resistor?

A

the time taken for current (or charge or voltage) to fall to 1/e of its initial value

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7
Q

How do you calculate the total capacitance for capacitors in parallel?

A

CT = C1 + C2 + C3 + ….

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8
Q

How do you calculate the total capacitance for capacitors in series?

A

1/CT = 1/C1 + 1/C2 + 1/C3….

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9
Q

If capcitors are connected in series what quantitiy is the same for all capacitors?

A

Charge stored

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10
Q

If capcitors are connected in parallel what quantitiy is the same for all capacitors?

A

p.d.

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11
Q

What is representd by the area under a p.d. - charge graphs?

A

Electrical energy transferred OR work done.

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12
Q

What is represented by the gradient of a charge-p.d. graph for a capacitor?

A

Capacitance

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13
Q

Out of Q, V and I which variable(s) follow the relationship x = x0 e-(t/RC) when discharging a capacitor?

A

Q, V and I

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14
Q

Out of Q, V and I which variable(s) follow the relationship x = x0 e-(t/RC) when charging a capacitor?

A

I

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15
Q

Out of Q, V and I which variable(s) follow the relationship x = x0 (1 - e-(t/RC) ) when charging a capacitor?

A

Q and V

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16
Q

What is meant by the constant-ratio nature of exponential decay?

A

In equal time intervals the quantity decreases by equal factors.

17
Q

How much charge remains after 1 time constant when discharging a capacitor?

A

e⁻¹ OR 0.37 OR 37%

18
Q

How much charge remains after* n* time constants when discharging a capacitor?

A

e^(-n)

19
Q

What is represented by the gradient of charge-time graph when charging a capacitor?

A

Charging current

20
Q

State a two uses of capacitors.

A

Energy storage e.g. for camera flashes, spot welding…; timing circuits; voltage smoothing; audio filters.

21
Q

What does the direction of an electric field line show?

A

The direction of the force exerted on a positive test charge.

22
Q

What does the density of electric field lines show?

A

Field strength.

23
Q

When is the equation E = V/d used?

A

To find the uniform field strength between two parallel plates.

24
Q

State Coulomb’s law in words.

A

The force between two point charges is proportional to the product of the two charges and inversely proportional to the square of their separation distance.

25
Q

What is the relationship between the electrostatic force between two point charges and their seperation distance?

A

It is inversely proportional to the square of separation OR inverse square law

26
Q

What is the relationship between potential and distance from a point charge?

A

Potential α 1/distance

27
Q

What is a uniform electric field?

A

A region of space in which the electric field strength is the same at all points

28
Q

What is a radial field?

A

An electric field generated by a point charge OR a field that obeys the inverse square law.

29
Q

Is electric field strength a vector or a scalar quantity?

A

Vector

30
Q

Is electrical potential a vector or scalar quantity?

A

Scalar

31
Q

State a similarity between electric and gravitational fields.

A

Both obey inverse square law for field strength/an inverse proportionaility between potential (around a point mass/charge). Both have infinite range.

32
Q

What are the differences between electric and gravitational fields (at least 2)?

A

Gravitational fields act on masses, electric fields on charges: electric fields are much stronger that gravitational fields: electric fields can be attractive or repulsive, gravitational fields are always attractive: potential is always negative in a gravitational field.

33
Q

When is the equation V = Q / (4πε₀r) used?

A

To find the potential around a point charge/in a radial field.

34
Q

When is the equation C = 4πε₀R used?

A

To calculate the capacitance on an isolated sphere.

35
Q

What is represented by R in the equation C = 4πε₀R used?

A

he radius of an isolated sphere.

36
Q

What is the relationship between electric potential energy and electric potential?

A

EPE = V x q where q is the charge in the field.

LAET A-level OCR Physics A 2023 (15 decks)

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