物理靜電學 DSE、CE 選擇題

1.

Spheres P and Q hanging apart, and spheres R and S hanging close together, on threads of the same length

In the above figures, $P$ , $Q$ , $R$ and $S$ are identical light conducting spheres and they are hanging freely by insulating threads of the same length. Which of the following deductions is/are correct ?

(1)

P

and

Q

must carry like charges.

(2)

R

and

S

must carry unlike charges.

(3)

P

and

Q

must carry the same amount of net charges.

2.

A rubbed plastic ruler can attract paper scraps before actually touching them. Which of the following descriptions about the charges on the rubbed ruler and the original charges on the paper scraps are possible ?

(1)The ruler and the paper scraps carry opposite charges.

(2)Both the ruler and the paper scraps are uncharged.

(3)The ruler carries charges and the paper scraps are uncharged.

3.

Two conducting spheres are hanging freely in air by insulating threads. In which of the following will the two spheres attract each other ? Note : 'N' denotes that the sphere is uncharged.

Three arrangements of two hanging spheres: (1) + and -, (2) + and N, (3) - and N

4.

Three conducting spheres are suspended by separate nylon threads. When any two of them are brought near each other, they attract each other. Which of the following deductions is correct ?

5.

Four point charges at the vertices of a square (+ top-left, - top-right, - bottom-left, + bottom-right) with point charge C at the centre

Four point charges of equal magnitude are placed at the four vertices of a square. The signs of the charges are as shown. A point charge $C$ is placed at the centre of the square. What will be the direction of the resultant electrostatic force, if any, acting on $C$ ?

6.

A stream of water from a tap attracted towards a plastic ruler

A plastic ruler is placed close to a stream of running water coming from an insulated tap. The stream of water is attracted towards the ruler as shown above. Which of the following statements are correct ?

(1)The ruler carries an electric charge.

(2)The ruler and the running water are attracting each other with forces of equal magnitude.

(3)Both positive and negative charges are induced on the running water

7.

Two charged spheres A and B hanging from a point on a ceiling by two identical nylon threads

Two charged spheres $A$ and $B$ hanging at a point on a ceiling by two identical nylon threads. They remain at rest as shown above. Which of the following statements must be correct ?

(1)Both spheres carry positive charges.

(2)The force acting on

B

by

A

is larger than the force acting on

A

by

B

.

(3)The mass of

A

is larger than

B

.

8.

Three insulated uncharged metal spheres X, Y, Z in contact with a negatively charged rod near X

Three insulated uncharged metal spheres $X$ , $Y$ and $Z$ are placed in contact as shown. A negatively charged rod is brought near $X$ and sphere $Y$ is then earthed momentarily. If the charged rod is still near $X$ , which of the following describes the charges on $X$ , $Y$ and $Z$ ?

Sphere $X$	Sphere $Y$	Sphere $Z$
positive	zero	zero
positive	zero	negative
positive	positive	positive
zero	zero	zero

9.

The following are the steps to charge an isolated metal sphere by induction, but they are in the wrong order.

(1)Removing the finger away from the metal sphere.

(2)Touching the metal sphere with a finger.

(3)Bringing a positively charged rod near the metal sphere.

(4)Removing the positively charged rod away from the metal sphere.

Which of the following shows the correct order ?

10.

A small conducting sphere is suspended by an insulated thread. When a positively charged rod is brought near the sphere, the sphere is attracted as shown. Which of the following is/are reasonable deduction(s) ?

(1)The sphere may carry a positive charge.

(2)The sphere may carry a negative charge.

(3)The sphere may be neutral.

Suspended sphere attracted towards a positively charged rod