A-level Electric current

What is current?

• ratio of charge to time the charge flow

• rate of flow of positive charge

• rate of flow of negative charge

• ratio of voltage to resistance

Which of the following represents the definition of 1 coulomb?

• 1 ampere x 1 second

• 1 ampere/1 second

• 1 joule/ 1 volt

• 1 watt x 1 second

A copper wire of cross-sectional area 2.0 mm² carries a current of 10 A. How many electrons pass through a given cross-section of wire in one second?

• $1.0\ x\ 10^1$

• $5.0x10^{26}$

• $6.3x10^{19}$

• $3.1x10^{25}$

The current in a component is reduced uniformly from 100 mA to 20 mA over a period of 8.0 s. What is the charge that flows during this time?

• 160 mC

• 320 mC

• 480 mC

• 640 mC

The flow of current in a conductor is given as

I = nqAv

Which of the following is not true?

• n is the number of electrons

• q is the charge flowing

• .A is the cross-sectional area of wire

• v is the average drift velocity of the charge carriers.

For a conductor and semiconductor of same dimension and carrying the same current, the drift velocity of charge carriers in semiconductor is larger than in conductor

• as conductor expand on heating

• as the number of charge carriers per unit volume for semiconductor is much less that that for conductor

• as cross-sectional area of conductor expand as current flows through it

• magnitude of charge carrier in semiconductor is larger than in conductor.

Which equation is used to define resistance?

• power = (current)² x resistance

• resistivity = resistance x area ¸length

• potential difference = current x resistance

• energy = (current)² x resistance x time

Which statement explains the shape of this graph?

• As the filament temperature rises, electrons can pass more easily through filament.

• It takes time for the filament to reach its working temperature.

• The power output of the filament is proportional to the square of the current through it.

• The resistance of the filament increases with a rise in temperature.

What is a correct statement of Ohm’s law?

• The potential difference across a component equals the current providing the resistance and other physical conditions stay constant?

• The potential difference across a component equals the current multiplied by the resistance.

• The potential difference across a component is proportional to its resistance.

• The potential difference across a component is proportional to the current in it providing physical conditions stay constant.

The three circuit elements are a metal wire at constant temperature, a semiconductor diode and a filament lamp.

Which is the correct answer?

• X = metal wire, Z = semiconductor diode, Y = filament lamp

• Y = metal wire, X = semiconductor diode, Z = filament lamp

• Y = metal wire, Z = semiconductor diode, X = filament lamp

• Z = metal wire, X = semiconductor diode, Y = filament lamp