IBPhysics: HLDPTopic Questions10. Fields (HL only)10.2 Fields at Work

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First teaching 2014

Last exams 2024

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Fields at Work (DP IB Physics: HL)

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10.2 Fields at Work

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10.2 Fields at Work

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1
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When a mass is moved against the force of gravity, work is done such that the change in work done, ΔW is equal to the change in gravitational potential ΔV.

Which line correctly identifies the equation and named variables for work done when moving a mass in a gravitational field?

  symbol equation word equation
A. Fs force × distance
B. FΔV force × change in gravitational potential
C. ms mass × distance
D. mΔV mass × change in gravitational potential

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    2
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    When a mass moves through a gravitational field the magnitude of the potential energy EP  changes. Which equation could be used to correctly calculate this?

    • increment E subscript p equals G M m open parentheses 1 over r subscript 1 minus 1 over r subscript 2 close parentheses

    • increment E subscript p equals G M m open parentheses negative 1 over r subscript 1 minus 1 over r subscript 2 close parentheses

    • increment E subscript p equals G M m open parentheses 1 over r subscript 1 plus 1 over r subscript 2 close parentheses

    • increment E subscript p equals G M m open parentheses 1 over r subscript 1 cross times 1 over r subscript 2 close parentheses

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    3
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    Two point charges q1 and 2q2 are separated by distance 2r.

    What is the value of the electric potential energy Ep?

    • E subscript p space equals space fraction numerator 2 q subscript 1 q subscript 2 over denominator 4 pi epsilon subscript 0 r end fraction

    • E subscript p space equals space fraction numerator q subscript 1 q subscript 2 over denominator 8 pi epsilon subscript 0 r end fraction

    • E subscript p space equals space fraction numerator q subscript 1 q subscript 2 over denominator 4 pi epsilon subscript 0 r end fraction

    • E subscript p space equals space fraction numerator 2 q subscript 1 q subscript 2 over denominator 8 pi epsilon subscript 0 r end fraction

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    4
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    An electric field can be defined in terms of the variation of electric potential at different points in the field.

    Which graph correctly represents this relationship?

    10-2-ib-hl-mcqs-easy-q4

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      5
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      Which quantity does the following statement define?

      The work done by moving a positive test charge from one point to another in an electric field.

      • Potential gradient

      • Electric field strength

      • Gravitational potential

      • Potential difference

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      6
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      Two parallel metal plates are separated by distance, d and have a potential difference of Ve.

      Which equation correctly gives the magnitude of the electric force acting on a stationary charged particle between the plates if the particle has a charge of Q?

      • F equals E over Q

      • F equals k fraction numerator q subscript 1 q subscript 2 over denominator d squared end fraction

      • F space equals space m a

      • F equals space fraction numerator Q V subscript e over denominator d end fraction

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      7
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      Read the following statements about the escape velocity on Earth. Which ones are correct?

      Escape velocity;

      1. Increases as the mass of the object increases
      2. Depends on the mass of the Earth and is not affected by the mass of the object
      3. Is defined as the minimum speed that allows an object to escape a gravitational field with no further energy input

      • I. only

      • I. and II.

      • II. and III.

      • III. only

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      8
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      The equation for linear orbital speed is

      v equals square root of fraction numerator G M over denominator r end fraction end root

      Which statement is a consequence of this equation?

      • Orbital speed is the same for all objects, regardless of their mass, when their orbital radius is the same.

      • Orbital speed is the same for all objects, regardless of their mass, when they orbit the same planet.

      • The gravitational constant, G, can be derived if orbital speed and radius are both known.

      • Time period, T can be derived from orbital speed and radius.

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      9
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      Gravitational and electrostatic forces are similar in many ways. Which statements are correct about both?

      1. Both electrostatic forces and gravitational forces are always attractive
      2. Both electrostatic forces and gravitational forces may be attractive or repulsive
      3. Both electrostatic forces and gravitational forces follow an inverse square law
      4. The equations used to calculate these forces rely on knowing certain universal constants

      • I and III only

      • III and IV only

      • I, II, and III only

      • II, III, and IV only

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      10
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      A charged particle in an electric field will experience a force on it that will cause it to move. The three particles X, Y and Z are experiencing a force which deflects their motion as shown. What three particles could X, Y and Z be?

      10-2-ib-hl-mcqs-easy-q10

        X Y Z
      A. beta-minus particle photon nucleus
      B. alpha particle neutron photon
      C. neutron electron alpha-particle
      D. electron beta-plus particle neutron

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        1
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        The mass of Jupiter is mJ and the mass of its moon Europa is mE. 

        If their radii is given by rJ and rE respectively, what is the ratio fraction numerator e s c a p e space v e l o c i t y space o f space E u r o p a over denominator e s c a p e space v e l o c i t y space o f space J u p i t e r end fraction?

        • square root of fraction numerator m subscript E space space r subscript E over denominator m subscript J space space r subscript J end fraction end root

        • square root of fraction numerator m subscript E space space r subscript J over denominator m subscript J space space r subscript E end fraction end root

        • square root of fraction numerator m subscript J space space r subscript J over denominator m subscript E space space end subscript r subscript E end fraction end root

        • square root of fraction numerator m subscript J space space r subscript E over denominator m subscript E space space end subscript r subscript J end fraction end root

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        2
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        A satellite of mass 2000 kg is in the Earth’s gravitational field. It moves radially from a point where the gravitational potential is –40 MJ kg–1 to a point where the gravitational potential is –10 MJ kg–1. What is the direction of movement of the satellite and the change in its gravitational potential energy?

         

        Direction of movement of satellite

        Change in gravitational potential energy / GJ

        A.

        Parallel to a field line

        60

        B.

        Antiparallel to a field line

        30

        C.

        Along an equipotential

        30

        D.

        Antiparallel to a field line

        60

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          3
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          Which graph shows how the kinetic energy EK, the potential energy EP and the total energy E of the international space station varies with distance x from the centre of Earth?

          10-2-hl-mcq-medium-q3

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            4
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            A probe is launched from the surface of the Earth, which has a radius R, at half the required escape velocity. 

            What is the maximum height from the surface the probe will reach, before returning to the ground (with a bang)? 

            • R

            • R over 2

            • R over 3

            • R over 4

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            5
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            The radius of the Sun is approximately 700 000 km. If all of its mass were compressed into a certain radius, it would collapse into a black hole, which is known to be a body from which "not even light can escape".

            Which length gives the best estimate for the radius at which the Sun's mass would collapse into a black hole?

            Use the following data: 

            • Mass of the Sun = 2 × 1030 kg
            • Speed of light = 3 × 108 m s–1
            • Gravitation constant = 6.67 × 10–11 N m2 kg–2

            • 3 mm

            • 3 cm

            • 3 km 

            • 3 × 105 km 

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            6
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            The graph shows the variation of gravitational potential V with distance r from the centre of a spherical planet of mass M and radius R0. 

            10-2-hl-mcq-medium-q6

            Which statement best describes how to determine the gravitational field strength at a distance r = R from the planet?

            • The area enclosed by the horizontal axis, the line r = R0, the line r = R, and the curve 

            • The gradient at the point r = R

            • The inverse of the gradient at the point r = R

            • The negative of the gradient at the point r = R

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            7
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            The gravitational field strength is g and the gravitational potential is V at the surface of Earth, which has a radius of r.  

            Which row in the table gives the correct value of the gravitational field strength and the gravitational potential at a height of 2r from Earth's surface? 

             

            Gravitational field strength

            Gravitational potential

            A.

            g over 3

            V over 3

            B.

            g over 4

            V over 2

            C.

            g over 9

            V over 3

            D.

            g over 16

            V over 2

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              8
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              A particle of charge q is at point J in a uniform electric field of strength E. It is moved along a straight line joining point J to point K which is at an angle of Φ to the field lines, as shown in the diagram below. 

              10-2-hl-mcq-medium-q8

              If the length of the path is JK, what is the change in electric potential energy of the charge q between J and K? 

              • EqJK cos Φ

              • EqJK sin Φ

              • Eq tan Φ

              • EqJK 

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              9
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              Two positively charged particles, q1 and q2, are released from rest half-way between two oppositely charged parallel plates in a vacuum. The particles strike the negatively charged plate at the same time. 

              10-2-hl-mcq-medium-q9

              Neglecting gravitational effects, which of the following statements is correct? 

              • The particles have the same charge only

              • The particles have the same mass only

              • The particles have the same mass and charge

              • The particles have the same charge to mass ratio

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              10
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              Two charged parallel metal plates, X and Y, are separated by a distance of 2.0 m. X is charged to a potential of –180 V and Y is charged to a potential of +180 V. 

              10-2-hl-mcq-medium-q10

              What is the magnitude and direction of the electric field strength at a point exactly mid-way between plates X and Y? 

               

              Magnitude of electric field strength / V m–1

              Direction

              A.

              180

              To the right

              B.

              180

              To the left

              C.

              360

              To the right

              D.

              360

              To the left

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                1
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                A proton with velocity of 1.5 × 107 m s−1 moves normally into a uniform magnetic field of flux density 0.30 T. Which is the best estimate of the radius of curvature of the path of the proton?

                • 5 × 10−38 m

                • 5 × 10−3 m

                • 5 × 10−1 m

                • 5 m

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                2
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                The diagram shows a uniform electric field in which equipotential lines are placed 3.0 cm apart.

                     qu-15

                A charge of –6.0 nC is placed at the equipotential line X.

                Which of the following statements is correct?

                • The charge is in an electric field directed from Z to X and has a gain of 4.8 × 10–7 J of kinetic energy moving from X to Z

                • The charge is in an electric field directed from X to Y and has a loss of 2.4 × 10–7 J of kinetic energy moving from Y to Z

                • The charge is in an electric field directed from X to Y and has a gain of 1.2 × 10–7 J of kinetic energy moving from Y to Z

                • The charge is in an electric field directed from X to Z and has a loss of 1.2 × 10–7 J of kinetic energy moving from Y to Z

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                3
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                The diagram shows four point charges at the corners of a square of sides 4a.

                qu-14

                What is the electric potential at P, the centre of the square?

                • negative fraction numerator Q over denominator pi epsilon subscript 0 2 square root of 2 a end root end fraction

                • negative fraction numerator Q over denominator pi epsilon subscript 0 4 square root of 2 a end root end fraction

                • negative fraction numerator Q over denominator 2 pi space epsilon subscript 0 space a end fraction

                • negative fraction numerator Q over denominator 4 pi space epsilon subscript 0 space a end fraction

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                4
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                The Earth has radius, r and mass M. Which expression could be used to calculate the minimum time, T of one Earth-day for the material at the equator to just remain on the surface?

                • fraction numerator 4 pi squared space m r over denominator G M end fraction

                • fraction numerator 2 pi space r cubed over denominator G M end fraction

                • fraction numerator 4 pi squared space r cubed over denominator G M end fraction

                • space 2 pi square root of fraction numerator r cubed over denominator G M end fraction end root

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                5
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                A space probe with mass m is launched from the surface of the Earth’s equator into orbit. The total energy Et given to the space probe is:

                E subscript t equals fraction numerator 3 G M m over denominator 4 space r subscript E end fraction

                where G is the gravitational constant and M and rE are the mass and radius of Earth.

                What is the height of the space probe’s orbit above the Earth’s surface?

                • rE

                • 2rE

                • 3rE

                • 4rE

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                6
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                Two satellites, X and Y, of equal mass, orbit a planet at radii R and 2R respectively.

                Which one of the following statements is correct?

                • X has more kinetic energy and more potential energy than Y

                • X has more kinetic energy and less potential energy than Y

                • X has less kinetic energy and more potential energy than Y

                • X has less kinetic energy and less potential energy than Y

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                7
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                A cable used in high-voltage electrical transmission has a radius of 3.0 mm. The diagram shows the circular cross-section of the cable with electrical field lines denoting areas of equipotential.

                In the instant shown the potential of the cable is + 600 000 V.

                cable-potential

                Assuming that the diagram has been drawn to scale, what is the the potential gradient near the surface of the cable?

                • -25 × 106 V m−1

                • -50 × 106 V m−1

                • -75 × 106 V m−1

                • -125 × 106 V m−1

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                8
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                Two identical negative point charges, P and Q, are separated by a distance of 6.0 mm. The resultant electric potential at point M, which is mid–way between the charges, is –40 V.

                10-2-ib-hl-mcq-q8

                What would be the resultant electrical potential at a point 2.0 mm closer to Q?

                • –90 V

                • –72 V

                • –60 V

                • –48 V

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                9
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                Observations are made on two separate planetary system's suns of mass M1 and mass M2.

                Their orbiting planets, P1 and P2 have masses of m1 and m2, and are observed to have identical orbits in shape and magnitude. P1 completes an orbit in a quarter of the time taken by P2.

                Which statement can astronomers reasonably deduce?

                • M1 = M2 and 9m1 = m2

                • M1 = 16 M2 and m1 = m2

                • 4 M1 = M2 

                • M1 = 16 M2 

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                10
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                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?

                B8pe0foI_qu-12

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