Describing Fields (DP IB Physics: HL)

A test mass m moves between position A and B as shown, in the presence of a source mass M. 

Which of the following statements is correct? 

A positive charge Q is deposited on the surface of a small sphere. The dotted lines represent equipotentials.

A small positive point charge is moved from point P closer to the sphere along two different paths X and Y. What is the best comparison of the work done along X and Y, W_X and W_Y?

Two point charges are at rest as shown. Four positions, each of distance r from the nearest point charge, are marked in the image. 

At which position is the electric field strength greatest?

Equipotential surfaces corresponding to lines of constant gravitational potential are conventionally drawn so that the difference in potential between any two adjacent surfaces is the same. 

Consider the equipotential surfaces for a spherical mass M. Which of the following statements is incorrect? 

A helium nucleus is accelerated from rest across a potential difference of 5.0 kV.

If m_p and m_n is the rest mass of a proton and neutron respectively, which expression for the final velocity of the nucleus is correct? 

A small point charge +q descends vertically into a region where there is an electric field. The equipotentials of this field are shown. 

What is the subsequent path followed by the particle?  

Which diagram shows a correct equipotential line due to two point charges P and Q of equal sign? 

Four point charges, W, X, Y and Z, are fixed to the edges of a square with midpoint O.

W, X and Z are negatively charged, and Y is positively charged. What is the direction of the resultant electric field at O? 

The diagram shows equipotential lines around two sources. 

Possible combinations of sources for this potential field are: 

1. Two equal point charges of the opposite sign
2. Two equal point charges of same sign
3. Two equal point masses

What is/are the possible source(s) for the equipotential lines? 

The shape of equipotential surfaces in the gravitational field depends on perspective. 

The image below shows equipotential surfaces (represented by dotted lines) due to the Earth’s gravitational field in a ‘local’ frame of reference (close to the Earth’s surface) and in a ‘non–local’ frame of reference (far from the Earth’s surface):

Which line, A to D, in the table shows the variation of gravitational potential V with radial distance r from the Earth’s surface?

You may assume each dotted line represents equal changes in potential ΔV and that r_E represents the radius of the Earth.

The relative positions of a binary star system is shown below:

The line XY joins the surface of the star of mass m to the surface of the star of mass M > m. Assume the stars have the same diameter.

Which graph correctly represents the variation of the gravitational potential ϕ along the line XY? 

Planet Z, with centre O, is shown in the figure below.

The radial distances OP is equal to the OX, and OQ is equal to OY, such that PX and QY are loci of Planet Z.

Which of the following statements is incorrect?

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

Two points charges of +4Q and –Q are placed 150 mm apart.

 Which of the following graphs shows the variation of the potential V against the distance x along the line joining the two point charges?

Which of the following statements about gravitational fields is correct?

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 fourth corner?

Two objects X and Y of equal mass, m and distance, D apart move with a constant speed v in circular orbit about their common centre of mass CM. X has a charge of +6.0 nC and Y has a charge of –6.0 nC.

Which graphs shows the electric potential, V and gravitational potential, φ,  against position along the straight-line joining X and Y?

A positive charge is placed at S and a negative charge is placed at T. The electric potential at different points between the charges is shown below.

Which graph correctly shows the variation with x along the line ST of the electric field strength, E?

A weighted, positively charged sphere is released from rest, in a vacuum, between two parallel, vertical metal plates one at +100 V and the other grounded. The sphere is initially 4.0 cm from the edge of the grounded plate and 3.0 cm from the bottom of the plates. The sphere takes one of the paths P, Q, R or S and reaches the end of its trajectory in 60 ms.

By choosing the correct path, what is the speed of the sphere at the end of its trajectory?