Ch08 A-level Physics CIE (flipped)

Which direction do we always draw electric current ('conventional current') moving in?

Positive to negative

Which direction do electrons in a wire move?

Negative to positive

Electric current is the flow of what?

Charge

The equation that defines electric current

I = Q/t ....... I = current; Q = charge; t = time

What are the units of electric current?

amperes (amps)

What are the units of electric charge?

coulombs

What is the smallest possible charge that anything can have?

1.6x10^-19 C ...... (or the negative of this)

Which word means that electric charge comes in small units that cannot be subdivided?

quantised

Which word means the number of conduction electrons per cubic metre of a metal?

number density

Which word means the average velocity of the electrons as they move through the metal?

drift velocity

This equation is on the equation sheet. What do the letters mean? I = nAvq

I = current; n = number density; A = cross-sectional area; v = drift velocity; q = charge of the charge carriers

When deriving the equation that links current with cross-sectional area, which equation do we use to link volume of the wire and its cross-sectional area?

Volume = Area x length

When deriving the equation that links current with cross-sectional area, which equation do we use to link number of electrons and the volume of the wire?

Number of electrons = number density x volume

When deriving the equation that links current with cross-sectional area, which equation do we use to link total charge of the electrons and number of electrons?

Total charge = charge on one electron x number of electrons

When deriving the equation that links current with cross-sectional area, which equation do we use to link drift velocity and length of wire?

Drift velocity = length of wire / time to flow through the wire

What is an approximate value for the typical drift velocity of electrons in a wire?

1 millimetre per second

Is electric current a scalar or a vector?

Scalar

Write down the equation that links energy and voltage

V = W/Q ........... V=voltage; W=energy; Q=charge

Which word means the voltage when energy is LOST by the electrons?

Potential difference

Which word means the voltage when energy is GAINED by the electrons?

emf

Define potential difference

Energy transferred per unit charge

Define emf

Energy transferred per unit charge in driving charge around a complete circuit

Is voltage a scalar or a vector?

Scalar

Write down the equation that links voltage, current and resistance

V = I x R ......... V = potential difference; I = current; R = resistance

Define resistance

The ratio of potential difference to current

What are the units of resistance? (name and symbol)

Ohms (Ω)

Define the ohm

The resistance when a potential difference of 1V causes a current of 1A

The equation that links power, voltage and current

P = I V .......... P = power; I = current; V = voltage

The equation that links power, current and resistance

P = I^2 R ........... P = power; I = current; R = resistance