Electric current

The diagram illustrates an electron situated in a uniform electric field. In what direction will the field cause the electron to accelerate?

Feb/March 2016

At a particular distance from a single alpha particle, the electric field strength is $3.0 \times 10^7\,\text{N C}^{-1}$. What force acts on an electron when it is at that same distance from the alpha particle?

Feb/March 2016

A conductor of electricity has a resistance of $5.6\,\text{k}\Omega$. A potential difference (p.d.) of $9.0\,\text{V}$ is applied across its two ends. How many electrons pass a point in the conductor in one minute?

Feb/March 2016

An electric current $I$ appears in the list of formulae on page 3 as $I = Anvq$. What does each symbol stand for in the expression for an electric current in a metal wire?

Feb/March 2017

Charge carriers, each carrying charge $q$, travel along a wire of fixed length. The number density of the charge carriers in the wire is $n$. What other information is needed, for this wire, to find the average drift velocity of the charge carriers in terms of $n$ and $q$?

Feb/March 2018

The diagram illustrates the electric field close to a point charge, together with two electrons X and Y. Which row gives the forces on X and on Y?

Feb/March 2019

The electric current in a wire can be determined from the equation $I = Anvq$. Which statement is incorrect?

Feb/March 2019

A particle sits within a uniform field, and the force on it points in the direction opposite to the field. What type of field is this, and what property of the particle does the field act on?

Feb/March 2020

Electrons travel through a vacuum from one metal plate to a different metal plate. This produces an electric current of $48\,\mu\text{A}$ between the plates. How many electrons are released from the first plate in a time of $5.0$ minutes?

Feb/March 2020

The electric current $I$ in a metal wire is described by the equation $I = Anvq.$ What is represented by the symbol $n$?

Feb/March 2021

For a wire that carries current, the current may be found using the equation shown. $I = Anvq$. What is the meaning of $n$?

Feb/March 2022

Over a period of $24$ hours, $6.0 \times 10^{23}$ free electrons pass one point in a wire. What is the wire’s average current?

Feb/March 2022

In a vacuum, a radioactive source emits a beam of $\alpha$-particles. The mean current due to the $\alpha$-particles in the beam is $1.5 \times 10^{-9}\,\text{A}$. The beam strikes a metal target. What is the mean number of $\alpha$-particles reaching the metal target in a time of $3.0\,\text{s}$?

Feb/March 2024

The charge carriers in a metal wire are free electrons. Which statement about the charge on each free electron is correct?

Feb/March 2024

Two cylindrical conductors, X and Y, are made of the same material. They have the same length, but the diameter of Y is smaller than that of X. X and Y are joined in series to a cell. Which row compares the number of charge carriers per unit time passing through X with that through Y, and also compares the average drift speed of the charge carriers in X with that in Y?

Feb/March 2025

A metal electrical conductor has a resistance of $5.6\,\text{k}\Omega$. A potential difference (p.d.) of $9.0\,\text{V}$ is applied across its two ends. How many electrons pass through a point in the conductor in one minute?

Feb/March 2025

The diagram depicts a circuit junction where three wires, P, Q and R, are connected. The currents in P and Q are $1\,\text{A}$ and $3\,\text{A}$ respectively, in the directions indicated. How much charge passes a fixed point in wire R during a time of $5\,\text{s}$?

Feb/March 2025

A copper wire $P$ with a cylindrical shape and length $0.24\,\text{m}$ is illustrated in Fig. 6.1. The current in the wire is $0.85\,\text{A}$. The resistance of the wire is $3.3\,\text{m}\Omega$. The total number of charge carriers, $N$, in the wire is $2.6 \times 10^{22}$. The resistivity of copper is $1.8 \times 10^{-8}\,\Omega\,\text{m}$.

Feb/March 2025

In the diagram, the shaded region shows a uniform electric field pointing away from the observer (at right-angles into the plane of the paper). A horizontal beam of electrons enters the field and travels from left to right. By the field, in which direction is this beam deflected?

May/June 2010

In the diagram, the shaded region shows a uniform electric field pointing away from the observer (perpendicular into the plane of the paper). An electron beam travels horizontally into the field from left to right. In what direction does the field deflect this beam?

May/June 2010

In the diagram, the shaded region shows a uniform electric field pointing away from the observer (that is, at right angles into the plane of the paper). A horizontal beam of electrons enters the field, moving from left to right. In which direction does this beam get deflected by the field?

May/June 2010

Which row shows the conditions in which forces act on a charged particle in a uniform electric field?

May/June 2010

A copper wire with cross-sectional area $2.0\ \text{mm}^2$ carries a current of $10\ \text{A}$. How many electrons pass through one chosen cross-section of the wire in 1 second?

May/June 2011

A copper wire with cross-sectional area $2.0\,\text{mm}^2$ carries a current of $10\,\text{A}$. How many electrons pass across a particular cross-section of the wire in one second?

May/June 2011

A current of $10\,\text{mA}$ flows through a conductor for half an hour. What charge passes a point in the conductor during this interval?

May/June 2012

At what time does $1\,\text{C}$ of charge pass a point in an electrical circuit?

May/June 2012

Two copper wires that are equal in length but have different diameters carry the same current. Which statement correctly describes the movement of charged particles through the wires?

May/June 2012

A dipole consists of one negative charge and one positive charge with the same magnitude. The dipole's electric field is shown below. In what direction does the force act on an electron at point X?

May/June 2012

A conductor carries a current of $10\,\text{mA}$ for half an hour. What quantity of charge passes a point in the conductor during this period?

May/June 2012

A very small oil droplet of mass $6.9 \times 10^{-13}\,\text{kg}$ is stationary in an electric field of electric field strength $2.1 \times 10^{7}\,\text{N C}^{-1}$, as illustrated. The droplet’s weight is exactly counterbalanced by the electric force acting on it. Determine the charge on the droplet.

May/June 2014

Which diagram most accurately shows the electric field between two point charges with equal magnitude and opposite sign?

May/June 2015

The amount of charge a fully charged $12\,\text{V}$ car battery can provide is $100\,\text{kC}$. The starter motor of the car needs a current of $200\,\text{A}$ for an average time of $2.0\,\text{s}$. A fault means the battery does not recharge. What is the greatest number of times the starter motor of the car can be operated?

May/June 2016

What does the term coulomb mean?

May/June 2016

Electric current is the movement of charge carriers. The charge carried by them is quantised. Explain what is meant by quantised.

May/June 2016

The diagram illustrates the symbol for a wire through which a current $I$ flows. What is meant by this current?

May/June 2017

The current through a circuit component is $2.00\,\mu\text{A}$. How many electrons pass through the component in each second?

May/June 2017

Two metal plates are separated by a distance of $30\,\text{cm}$ in a vacuum. A current flows between the plates because electrons move at a steady speed of $1.5 \times 10^{6}\,\text{m s}^{-1}$. At every moment, only one electron is present in transit between the plates. What is the current between the plates?

May/June 2017

A particle carries a charge of $+2.0\,\text{mC}$ and is located in a vertical uniform electric field. The particle experiences an upward electric force of $1.0 \times 10^{-2}\,\text{N}$. What is the electric field strength?

May/June 2018

The current $I$ in a metal wire is described by the expression below. $I = Anvq$ What is meant by the symbol $n$?

May/June 2018

A germanium slice with cross-sectional area $1.0\,\text{cm}^2$ carries a current of $56\,\mu\text{A}$. The charge-carrier number density in the germanium is $2.0 \times 10^{13}\,\text{cm}^{-3}$. Each charge carrier has a charge equal to that of an electron. What is the mean drift velocity of the charge carriers in the germanium?

May/June 2018

Define the term force.

May/June 2018

Within an electrolyte, electric current is transported by charged particles, called ions, in solution. Which value cannot be the charge on an ion in solution?

May/June 2019

A wire is inserted into a circuit. At $R$, the wire has cross-sectional area $A$, whereas at $S$ it is $\frac{1}{2}A$. The current in the wire is constant. Charge $Q$ passes point $R$ in a time $t$. What charge passes point $S$ in the same time $t$?

May/June 2019

Which diagram shows the electric field line pattern produced by a combination of two positive charges?

May/June 2019

In the circuit diagram shown, the current is $3.2\,\text{mA}$. What is the direction of electron flow through resistor $R$, and what is the rate at which electrons flow through it?

May/June 2020

The number density of free electrons in copper is $8.0 \times 10^{28}\,\text{m}^{-3}$. A copper wire has diameter $0.42\,\text{mm}$. Determine the average drift speed of the free electrons in the wire when the current in the wire is $0.57\,\text{A}$?

May/June 2020

The unit used for electric charge is the coulomb. What does 1 coulomb represent?

May/June 2020

As illustrated, two copper wires are connected together and a current flows through them. Wire P has diameter $d$, whereas wire Q has diameter $2d$. What is the ratio $\frac{\text{average drift speed of the free electrons in wire P}}{\text{average drift speed of the free electrons in wire Q}}$ ?

May/June 2020

The current $I$ in a metal wire is expressed as $I = Anve$, where $v$ denotes the mean drift speed of the free electrons in the wire and $e$ is the elementary charge.

May/June 2020

Determine the electric field strength in a region in which a proton accelerates at $2.00\,\text{m s}^{-2}$ because of the field.

May/June 2021

Which two units are combined to define the coulomb?

May/June 2021

A charged particle is situated in a uniform force field. The force acting on the particle points in the opposite direction to the field. Identify the field and the charge on the particle.

May/June 2021

A metal conductor with a wedge shape, of length $L$, non-uniform width and constant thickness, is attached to a cell, as illustrated. Which graph most accurately indicates how the mean drift velocity $v$ of electrons in the conductor changes with distance $x$ from end X?

May/June 2021

An analogue ammeter with a range of $0$-$250\,\text{mA}$ has been placed in an electrical circuit. The diagram shows the ammeter’s display. What is the reading on the ammeter?

May/June 2021

A particle carries a charge of $+2.0\,\text{mC}$ and is placed in a vertical uniform electric field. The particle experiences an upward electric force of $1.0 \times 10^{-2}\,\text{N}$. Determine the electric field strength?

May/June 2021

A wire is $12\,\text{cm}$ long and has a total of $5.1 \times 10^{22}$ free electrons. If a potential difference is applied across the two ends of the wire, the free electrons drift with an average speed of $4.0 \times 10^{-6}\,\text{m s}^{-1}$. Calculate the current in the wire.

May/June 2021

A copper wire that is straight and has a diameter of $0.42 \times 10^{-3}\,\text{m}$ contains free electrons with a number density of $8.5 \times 10^{28}\,\text{m}^{-3}$. During one time interval, a charge of $0.15\,\text{C}$ passes along the wire. What is the mean displacement of the free electrons along the wire over this time interval?

May/June 2022

The diagram represents a metal block. Its sides have lengths $a$, $b$ and $c$, as indicated, and the block’s volume is $V$. Every charge carrier carries a charge of $-q$, and the number density of charge carriers in the metal is $n$. On average, each charge carrier needs time $t$ to travel through the block. What expression gives the current $I$?

May/June 2022

Wires X and Y are both made from the same metal. The diameter of wire Y is 2 times the diameter of wire X. Wire X, wire Y and a battery are joined in series. What is the ratio $\dfrac{\text{average drift speed of free electrons in wire X}}{\text{average drift speed of free electrons in wire Y}}$?

May/June 2022

A metal wire carries an electric current of $4.0\,\text{mA}$. How many electrons pass a given point in the wire during a time of $10\,\text{hours}$?

May/June 2023

Which type of charge can be transported by a charge carrier?

May/June 2023

A metal wire is joined between the terminals of a cell, causing a current to flow through the wire. Which statement is correct?

May/June 2023

In a circuit, a metal wire measures $1.8\,\text{m}$ in length and has a cross-sectional area of $1.5 \times 10^{-6}\,\text{m}^2$. The wire contains a total of $2.3 \times 10^{23}$ free electrons (charge carriers). A current flows in the wire so that $172\,\text{C}$ of charge passes a fixed point during $2.5$ minutes.

May/June 2023

The current in a filament lamp becomes smaller. State and explain what happens to the lamp’s resistance.

May/June 2023

A cylindrical wire has cross-sectional area $A$ and free-electron number density $n$. The wire carries current $I$, and the free electrons move with mean drift speed $v$. A second cylindrical wire has cross-sectional area $0.5A$ and free-electron number density $2n$. In this wire, the free electrons move with mean drift speed $2v$. What current is in the second wire?

May/June 2024

An electric current is produced by charge carriers that are moving. Which charge is impossible for a charge carrier to have?

May/June 2024

A resistor with a resistance of $200\,\Omega$ is connected to a supply with a p.d. of $4.00\,\text{V}$. How many electrons move into the resistor in $4.00\,\text{s}$?

May/June 2025

What would be a sensible estimate for the current in an electric kettle while it is operating?

May/June 2025

For a metallic conductor with cross-sectional area $A$, the current $I$ is expressed as $I = Anve$ where $e$ denotes the elementary charge and $v$ is the average drift speed of the conduction electrons. What does the symbol $n$ stand for in this equation?

May/June 2025

Which charge cannot be carried by a charge carrier?

May/June 2025

A lamp has a resistance of $10\,\Omega$, and the potential difference across it is $6.0\,\text{V}$. In a period of 24 hours, how many electrons pass through the lamp?

May/June 2025

State and explain what effect, if any, the resistance of a filament wire in a lamp has as the current in the wire falls.

May/June 2025

The current in the circuit shown is $4.8\,\text{A}$. In which direction do electrons flow through the resistor $R$, and at what rate do they pass through it?

Oct/Nov 2010

If a wire carries no current, which statement about the conduction electrons in that wire is correct?

Oct/Nov 2010

In the circuit shown, the current is $4.8\,\text{s}^{-1}$. In which direction do electrons move through resistor $R$, and at what rate do they move?

Oct/Nov 2010

Four circuits are assembled using a cell, an ammeter and two resistors with equal resistance. Apart from the resistors, none of the other components in the circuits has resistance. In which circuit will the ammeter give the largest reading?

Oct/Nov 2011

Three resistors with resistances $R$, $2R$ and $3R$ are connected in parallel. If $I$ is used for the current in the resistor of resistance $R$, which row shows how the currents in the resistors are related?

Oct/Nov 2011

Three resistors with resistances $R$, $2R$ and $3R$ are joined in parallel. Using $I$ to stand for the current in the resistor of resistance $R$, which row shows the relationships between the currents in the resistors?

Oct/Nov 2011

A particle is placed in a uniform field. The force on the particle acts in the direction opposite to the field. What field is the particle in, and which property of the particle does the field act on?

Oct/Nov 2013

A particle is located in a uniform field. It experiences a force in the direction opposite to the field. Which field is the particle in, and which property of the particle is being acted on by the field?

Oct/Nov 2013

The current in a component falls evenly from $100\,\text{mA}$ to $20\,\text{mA}$ in $8.0\,\text{s}$. What charge passes in this interval?

Oct/Nov 2013

An electric current travels from a thick copper wire through a length of thinner copper wire and then into another thick copper wire, as shown. Which statement correctly describes the current and the speed of the electrons in the wires?

Oct/Nov 2013

Unevenly charged regions form inside a cloud, as shown. For region $X$, which diagram shows the direction of the electric field and the initial direction in which electrons would move?

Oct/Nov 2014

Which unit has the same magnitude as a coulomb (C)?

Oct/Nov 2015

For two point charges $q_1$ and $q_2$ separated by a distance $r$, the force $F$ is described by the equation $F = \dfrac{k q_1 q_2}{r^2}$ in which $k$ is a constant. What are the SI base units of $k$?

Oct/Nov 2016

The diagram illustrates a junction in a circuit at which three wires $P$, $Q$ and $R$ join. The currents in $P$ and $Q$ are $1\,\text{A}$ and $3\,\text{A}$, respectively, in the directions indicated. What quantity of charge flows past a fixed point in wire $R$ during a time of $5\,\text{s}$?

Oct/Nov 2016

A current of $2.0\,\text{A}$ flows through a wire for $1.0\,\text{hour}$. How many electrons pass a point in the wire during this interval?

Oct/Nov 2016

The current in the circuit diagram shown is $3.2\,\text{mA}$. What is the direction of electron flow through the resistor $R$, and what is their rate of flow?

Oct/Nov 2017

Two copper wires are connected end to end and a current flows through them, as shown. Wire P has diameter $d$ and wire Q has diameter $2d$. What is the ratio $\displaystyle \frac{\text{average drift speed of the free electrons in wire P}}{\text{average drift speed of the free electrons in wire Q}}$?

Oct/Nov 2017

The conduction-electron number density in copper is $8.0 \times 10^{28}\,\text{m}^{-3}$. For a copper wire with diameter $0.42\,\text{mm}$ carrying a current of $0.57\,\text{A}$, what is the mean drift speed of the electrons?

Oct/Nov 2017

State the meaning of an electric current.

Oct/Nov 2017

A charged particle is located in a uniform force field. The force on the particle acts in the direction opposite to that of the field. What is the field, and what is the charge on the particle?

Oct/Nov 2018

If a current of $5.0\,\text{A}$ flows through a copper wire, the mean drift speed of the free electrons is $8.0 \times 10^{-4}\,\text{m s}^{-1}$. What is the mean drift speed in another copper wire that has twice the diameter and a current of $10.0\,\text{A}$?

Oct/Nov 2018

Which two units are involved in defining the coulomb?

Oct/Nov 2018

The current $I$ in a copper wire can be determined by using the equation shown. $I = Anvq$. What does the symbol $v$ stand for?

Oct/Nov 2018

The current $I$ in a metal wire is represented by $I = Anve$. State what the symbols $A$ and $n$ represent.

Oct/Nov 2018

State what is meant by the coulomb.

Oct/Nov 2018

A metal plate with constant thickness is linked to a cell, as illustrated. Electrons travel in a clockwise direction round the circuit. Which statement about the metal plate is correct?

Oct/Nov 2019

The diagram indicates the direction of current through a metal block. Charge carriers enter the block via the face PQRS and exit from the face opposite it. The number density of charge carriers is $n$. Each charge carrier carries charge $e$. The mean drift speed of the charge carriers is $v$. Which expression gives the current in the block?

Oct/Nov 2019

For a wire carrying a current of $5.0\,\text{A}$, the mean drift speed of the conduction electrons is $7.4 \times 10^{-4}\,\text{m s}^{-1}$. Which row shows a possible cross-sectional area and number of conduction electrons per unit volume for this wire?

Oct/Nov 2019