5054 Physics Random Questions [4]

5054 Physics 
Random Structured Questions

[I recommend that you try to answer the questions in this link first, then scroll down to the responses to questions below.]

1    The circuit shown in Fig. 1.1 uses a 12 V battery. A and B are identical lamps, each designed to work from a 6 V supply.

Fig. 1.1

(a) Switch S is open, as shown in Fig. 1.1.

(i) State the value of

1. the potential difference p.d. across S,

p.d. = 0 V [1]

2. the reading on the voltmeter.

reading = 0 V. [1]

(ii) Comment on the brightness of the two lamps.

Both lamps will not giving off light. [1]

(b) Switch S is now closed.

(i) State the new reading on the voltmeter.

new reading = 6 V [1]

(ii) Comment on the brightness of the two lamps.

The two lamps are equally bright. [1]

(iii) Under these conditions, each lamp has a resistance of 18 Ω.

Calculate the current in each lamp.

The circuit is series and so the current passing any component must be the same as the total current.

total current = total voltage / total resistance

total current = 12 V / 36 Ω

current = 0.33 A [3]

 (c) With switch S open, lamp B is connected in parallel with lamp A. With no current, each lamp has a resistance of 1.8 Ω.

(i) Calculate the value of the combined resistance of A and B.

1 / R = 1 / 1.8 Ω + 1 / 1.8

1 / R = 2 / 1.8 Ω

R = 0.9 Ω 

combined resistance = 0.9 Ω [2]

 (ii) State why it would not be wise to close S when A and B are connected in parallel.

This is because, when S is close, there will be current already as soon as one of the resistor has already been connected.

[1]

[Total: 11]

2    (a) State the law of attraction and repulsion between electrostatic charges.

Like charges repel. Unlike charges attract. [2]

(b) Sometimes, when people have been riding in a car, they get an electric shock from the door handle as they get out of the car.

Suggest why this happens.

Net charges have been accumulated in the door handle due to friction. These charges find a path to flow between the handle and the ground when a person touches it. As the body of the person is the path, the person gets electric shock.

[2]

(c) A plastic rod is rubbed with a cloth and becomes positively charged. After charging, the rod is held close to the suspended table-tennis ball shown in Fig. 2.1. The table-tennis ball is covered with metal paint.

Fig. 2.1

(i) Describe what happens to the charges on the metal-painted table-tennis ball as the 

     positively-charged rod is brought close to the ball.

Negative charges move to the right side part of the ball while positive charges are at the left side part.

[1]

  (ii) The ball is attracted towards the charged rod.

Explain why this happens.

The attractive force between the negative charges at the right side of the ball and the rod is greater than the repulsive force between the positive left side of the ball and the rod

[2]

(iii) When it is a few centimetres away from the rod, the ball is briefly touched by a wire connected to earth.

In terms of the movement of charges, describe what happens to the charge on the ball.

Initially, the net charge on the ball is zero. It is just that it is polarized i.e. separated between the sides. When then polarized negative side is the one touched, electrons flow from ball to ground. If the one touched by the wire is the positive left side, electrons flow from Earth to the ball. In any case, the ball will be having a non-zero net charge.

[2]

[Total: 9]

3    (a) Fig. 3.1 represents a permanent magnet. 

Fig. 3.1 

Carefully draw on Fig. 3.1 to show the pattern and direction of magnetic field lines around the magnet. 

[Lines/Arrows drawn from N pole to S pole. These arrows should be spaced such that they are closer to each other at regions close to the magnet and that the lines don't cross each other.

[2]

(b) Fig. 3.2 shows a simplified circuit diagram for an electric oven. The oven contains a fan driven by a motor.

Fig. 3.2

(i) On Fig. 3.2, circle the symbol representing the heater. 

This symbol should be circled.

[1]

(ii) Fig. 3.2 includes a variable resistor. 

 Explain the function of the variable resistor in this circuit.

     The variable resistor changes resistance so as the potential difference and current passing through the heater changes.

 [2]

(iii) The potential difference across the motor is 250 V. The current in the motor is 2.0 A.

       Calculate the resistance of the motor.

R = V / I

R = 250 V / 2.0 A

R = 125 Ω

resistance = 125 Ω [3]

(iv) State the name of component X and explain how it contributes to the safety of the 

          user.

name of component X fuse

explanation it melts of open the circuit when the current goes very high

[2]

Total [10]