10 Simple physics multiple choice problems 1. Which of these statements about el

Question

10 Simple physics multiple choice problems

1. Which of these statements about electric field lines is incorrect? (a) (b) (c) (d) (e) Electric field lines never cross Electric field lines can never be parallel to each other The electric field is stronger where the field lines are closer together Electric field lines always start from positive charges (or from infinity) Electric field lines point in the opposite direction of the force on negatively charged particles Consider a proton with a positive charge, traveling to the right and entering an electric field as shown in the figure. When inside the electric field what hap 2. pens to the proton? (a) The proton speeds up as soon as it enters the field and then travels with constant speed. (b) The proton speeds up continuously while inside the field. (c) The proton slows down as soon as it enters the field and then travels with constant speed. (d) The proton slows down continuously while inside the field. (e) There will be no change in the proton's speed. 3. Consider an electron with a negative charge, traveling towards C and entering an electric field as shown in the figure. When inside the electric field what happens to the electron? (a) The electron gets deflected towards A. (b) The electron gets deflected towards B (c) The electron continues to travel towards C. (d) The electron stops as soon as it enters the electric field. (e) The electron gets reflected and travels in a direction opposite to the original direction

Explanation / Answer

1- b) electric field lines can be parallel, but they cannot cross each other. All the rest of the statements are true except b

2) b) as proton enters an electric force acts on proton in the direction of field hence proton acclerates continuously.

3) a) since force on negative charge acts opposite to field hence electron will deflect towards A

4) c) The right ball will induce charge on front surface of left ball and will attract it hence both balls will fall at equilibrium at c

5) b) both charges will attract charge q and their horizontal components will cancel each other and vertical down components will add up.

6) d) -2q charge will attract q and +2q will repel hence their vertical components will cancel each other and horizontal force towards left will add up

7) c) Force on positive charge will acts in direction of field i.e. downwards hence tension = gravity + electric force

hence tension will be greater than mg

8) c) E = 1/r2  hence on making r = 3r E becomes 9E

9) c) since field lines points away from positive charge and towards negative charge hence B will be negative and A will be positive

10) b) Since direction of electric field due to both charges are opposite at points B and C only and weakness in field due to less magnitude of charge Q is compensated by smaller distance at B compared to charge 2Q

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