Electric Fields (DP IB Physics: SL)

Two separated, identical conducting spheres X and Y of charge –8 μC and +12 μC respectively, are brought into brief contact and then separated. What is the final charge distribution on X and Y?

Which of the following statements about electric fields and potential differences is incorrect?

A proton of mass m_p and charge q is accelerated from rest across a potential difference, V of 5 × 10^–2 V. What is the best estimate for the magnitude of the proton’s final velocity, v_p?

The Tolman-Stewart experiment sought to find evidence that mobile charge carriers inside conducting metals are negatively charged.

It involved exploiting the inertia of ‘free’ charge carriers in the conductor. If the conductor was suddenly accelerated, a potential difference would be set up.

Assuming positive charges are fixed in place and mobile charge carriers are negative, which of the following statements about the Tolman-Stewart experiment is incorrect?

A point charge q is placed near a large spherical charge Q = 10q. What is the magnitude of the force experienced by q and Q and the magnitude of the electric field E created by Q at the position of q?

Two identical point charges q create a resultant electric field at X.

The line XY is a perpendicular bisector of the line joining both point charges.

Which vector most accurately depicts the direction of the resultant electric field at X?

The electron drift speed in a copper wire of diameter 2.0 mm is 3 × 10^–4 m s^–1. Typically, the number of free electrons per unit volume for copper is on the order of magnitude 10²⁸ m^–3. What is the best estimate for the current in the wire?   

A conducting wire, carrying current flowing from X to Y, has a non-uniform cross-sectional area.

Which statement is incorrect?

Two charges, Q₁ = q and Q₂ = 4q are separated by a distance r and exert a force of magnitude F on each other. By what factor does the magnitude of the force change if the charge on Q₁ doubles and the separation distance trebles?

What is the definition of electric current?

An ion of mass m kg carrying a charge of –Q pC travels horizontally with a kinetic energy of E_k = 10 eV. 

It enters a uniform vertical electric field of strength V kV m^–1, which is directed downwards and acts over a horizontal distance of 100 cm.   

Which row in the table below correctly shows the time for the ion to pass through the field, and the magnitude of the force on the ion?

Point charges, each of magnitude Q are placed at three corners of a square as shown in the diagram.

What is the direction of the resultant electric field at the corner with no charge?

Which one of the following cannot be used as a unit for electric field strength?

What is the electric field pattern between a conducting sphere and an earthed metal plate?

A +1.0 nC and −1.5 nC point charge are placed 6 cm apart at points P and Q. A point R is equidistant to both charges.

If an additional charge of +4.0 nC is supplied to both charges, what is the magnitude of the electric field at R and the direction of this field?

A student queries their answer after solving some physics problems. The teacher explains that the problem lies in the text book solutions, some of which are incorrect.

An extract from the mark scheme is shown below:

Without calculation, which answer does the teacher know to be an error?

Electric field strength is defined as 'the electric force per unit charge experienced by a small, positive point charge q'. 

Why is the test charge described as 'small'?

The electric potential at different points between two point charges is shown.

The electric field strength E varies along the line which connects P and Q.

Which graph correctly shows this variation, where x is the distance along the line PQ?

The diagram shows points X, Y and Z marked on a pattern of electric field lines. The spacing between X and Y and between Y and Z are the same.

The potential at X = 0 V and at Y is − 500 V.

What is a likely value for the potential at Z?