Electric circuits: Grade 11 Past Paper Questions

QUESTION 9. 9.1 The circuit diagram below shows three identical light bulbs X, Y and Z connected to a battery of negligible internal resistance. Two voltmeters, a switch S and two ammeters are also connected in the circuit as shown. SWITCH S IS OPEN. 9.1.1 How does the brightness of bulb X compare to that of bulb Y? Choose from X IS BRIGHTER, X IS DIMMER or X AND Y ARE EQUALLY BRIGHT. Give a reason for the answer. SWITCH S IS NOW CLOSED. 9.1.2 Which of the ammeters, A₁ or A₂, will have a higher reading? 9.1.3 Using relevant equations show that the reading on V₁ = 2V₂. BULB Y BURNS OUT WHILE SWITCH S IS CLOSED. 9.1.4 What effect will this have on the reading on voltmeter V₂? Choose from INCREASES, DECREASES or REMAINS THE SAME. Explain the answer. 9.2 An electric iron has specifications '220 V; 2000 W'. Calculate the cost of using the iron for 15 minutes if the cost of electricity is R2,80 per kWh.

QUESTION 10. Three resistors are connected in an electric circuit as shown in the diagram below. The ammeter and the connecting wires have negligible resistance. The voltmeters have very high resistance. The battery has an emf (ε) of 12 V and significant internal resistance (r). The voltmeters V₁ and V₂ read 8 V and 11,8 V respectively. 10.1 Calculate the reading on the ammeter. 10.2 Calculate the resistance of resistor R. 10.3 Calculate the internal resistance of the battery.

QUESTION 6. 6.1 State Ohm's Law in words. A battery with an internal resistance of 0,5 Ω and an unknown emf (ε) is connected to four resistors and a switch as shown in the circuit below. A high-resistance voltmeter (V) is connected across the battery. A₁ and A₂ are ammeters of negligible resistance. With switch S closed, the current passing through the 8 Ω resistor is 0,5 A, and resistor R delivers 12 W of power. 6.2 Calculate: 6.2.1 The reading on ammeter A₁ 6.2.2 The reading on ammeter A₂ 6.2.3 The emf of the battery (ε).

QUESTION 7. Three resistors and a light bulb are connected to a battery with an emf (ε) of 12 V and an unknown internal resistance (r) as shown in the diagram below. The ammeter and connecting wires have negligible resistance. The voltmeter reads 4,8 V when the switch is closed. 7.1 Define the term power in words. 7.2 Calculate the: 7.2.1 Effective resistance of the parallel combination 7.2.2 Reading on the ammeter 7.2.3 Internal resistance of the battery 7.2.4 Power dissipated by the light bulb. The switch is now opened. 7.3 Will the brightness of the bulb INCREASE, DECREASE or REMAIN THE SAME? Explain the answer.

QUESTION 9. 9.1 The circuit diagram below shows three identical light bulbs X, Y and Z connected to a battery of negligible internal resistance. Two voltmeters, a switch S and two ammeters are also connected in the circuit as shown. SWITCH S IS OPEN. 9.1.1 How does the brightness of bulb X compare to that of bulb Y? Choose from X IS BRIGHTER, X IS DIMMER or X AND Y ARE EQUALLY BRIGHT. Give a reason for the answer. SWITCH S IS NOW CLOSED. 9.1.2 Which of the ammeters, A₁ or A₂, will have a higher reading? 9.1.3 Using relevant equations show that the reading on V₁ = 2V₂. BULB Y BURNS OUT WHILE SWITCH S IS CLOSED. 9.1.4 What effect will this have on the reading on voltmeter V₂? Choose from INCREASES, DECREASES or REMAINS THE SAME. Explain the answer. 9.2 An electric iron has specifications '220 V; 2000 W'. Calculate the cost of using the iron for 15 minutes if the cost of electricity is R2,80 per kWh.

QUESTION 10. Three resistors are connected in an electric circuit as shown in the diagram below. The ammeter and the connecting wires have negligible resistance. The voltmeters have very high resistance. The battery has an emf (ε) of 12 V and significant internal resistance (r). The voltmeters V₁ and V₂ read 8 V and 11,8 V respectively. 10.1 Calculate the reading on the ammeter. 10.2 Calculate the resistance of resistor R. 10.3 Calculate the internal resistance of the battery.

QUESTION 3. A student conducts an experiment to investigate the relationship between the resultant force on an object, and acceleration. The experiment is set up using a trolley on an inclined runway, and a ticker timer that makes 50 dots every second. 3.1 Calculate the period of the ticker timer. When the trolley is released from the top of the runway, it moves down the slope and the following ticker tape is produced. 3.2 Briefly explain why the dots on the tape are initially close together. The slope of the runway is adjusted so that the dots become evenly spaced. 3.3 Was the ramp angle INCREASED or DECREASED? 3.4 What is the magnitude of the resultant force now acting on the trolley? 3.5 The trolley is now accelerated by first using one rubber band, then two rubber bands and finally three rubber bands. The rubber bands are stretched to the same extent each time. The three sets of results are plotted on a velocity-time graph shown below. 3.5.1 Which graph represents the results when THREE rubber bands were used? Choose from A or B. Give a reason for the answer. 3.5.2 Sketch a graph to show the relationship between the acceleration of the trolley and the force (in rubber band units) acting on the trolley.

1.8 The north pole of a bar magnet is pushed into a solenoid, as shown in the sketch below. The polarity of X on the solenoid and the direction of flow of the induced current through the solenoid will be... 1.9 The ampere second (A·s) is the unit for A. Current strength B. Quantity of charge C. Resistance D. Potential difference.

1.10 Which ONE of the following graphs represents the relationship between the total electrical energy transferred (W) and the electric current (I) in the element of a kettle? The resistance of the element and the time for which the current flows are constant.

1.4 Two charged objects repel each other with a force F when they are separated by a distance d. The distance between the same two charges is reduced to half. The new force, in terms of F, will now be... A. ¼F B. ½F C. 2F D. 4F. 1.5 The diagram below shows two light bulbs, P and Q, connected in series to a battery. If bulb P glows brighter than bulb Q, then the... A. resistance of bulb P is greater than that of bulb Q. B. resistance of bulb P is smaller than that of bulb Q. C. current through bulb P is smaller than that through bulb Q. D. current through bulb P is greater than that through bulb Q.

1.5 The diagram below shows a magnet that is moved towards a solenoid. Which ONE of the following combinations are CORRECT? A. North, X to Y B. North, Y to X C. South, X to Y D. South, Y to X. 1.6 Which ONE of the following graphs best represents the relationship between the electrical power (P) dissipated by a resistor and the potential difference (V) across the resistor if the resistance of the resistor remains constant? 1.7 Which ONE of the following is the unit of measurement for the rate of flow of charge? A. Coulomb B. Ampere C. Volts D. Watts.

QUESTION 1. 1.1 Two forces P and Q act at a point O. As the angle θ between P and Q varies, the MAXIMUM and MINIMUM resultant forces are 13 N and 3 N respectively. The magnitudes of the two forces are: A. 3 N and 10 N B. 16 N and 10 N C. 8 N and 5 N D. 10 N and 7 N. 1.2 A passenger standing in a moving bus moves forward when the bus suddenly stops. This can best be explained by A. Newton's First law of motion B. Newton's Second law of motion C. Newton's Third law of motion D. Newton's law of Universal gravitation. 1.3 A learner sits on a chair. What is the reaction force to her sitting on the chair? A. Force that the learner exerts on the chair. B. Weight of the learner. C. Force that the chair exerts on the learner. D. Force that the learner exerts on Earth. 1.5 A car, moving to the right along a rough horizontal surface, is brought to rest by a constant net force. If the motion to the right is taken as positive, which ONE of the following acceleration versus time graphs is correct for the motion of the car? 1.6 The graphs P, Q, R and S drawn below show a relationship between the force of attraction that two masses exert on each other and the inverse of the square of the distance between their centres. In which graph will the product of their masses be the largest? A. P B. Q C. R D. S. 1.7 The force of attraction between two charges q₁ and q₂ is F. If the distance between the charges is made four times smaller, then the new force of attraction will be... A. 0,5F B. 1,78F C. 2,5F D. 16F. 1.8 The north pole of a bar magnet is pushed into a solenoid, as shown in the sketch below. The polarity of X on the solenoid and the direction of flow of the induced current through the solenoid will be... 1.9 The ampere second (A·s) is the unit for A. Current strength B. Quantity of charge C. Resistance D. Potential difference. 1.10 Which ONE of the following graphs represents the relationship between the total electrical energy transferred (W) and the electric current (I) in the element of a kettle? The resistance of the element and the time for which the current flows are constant. QUESTION 2. Three forces Fₐ, F_B and F_C act on a point O in the directions shown in the diagram below. The magnitudes of Fₐ and F_C are 44 N and 31 N respectively. The magnitude of F_B is unknown. The forces are NOT drawn to scale. 2.1 Define the term resultant vector. The resultant of the three forces is 26,69 N at an angle of 25,82° to the horizontal, and lies in the first quadrant. 2.2 Calculate the magnitude of F_B. 2.3 Determine θ.

5.2 A square coil with sides of length 0,25 m contains 200 turns and is positioned perpendicular to a uniform magnetic field of magnitude 0,75 T. The coil is then quickly pulled from the field in 0,20 s, moving perpendicular to the magnetic field, to a region where there is no magnetic field. 5.2.1 State Faraday's Law of electromagnetic induction in words. 5.2.2 Calculate the emf induced across the coil. QUESTION 6. 6.1 State Ohm's Law in words. A battery with an internal resistance of 0,5 Ω and an unknown emf (ε) is connected to four resistors and a switch as shown in the circuit below. A high-resistance voltmeter (V) is connected across the battery. A₁ and A₂ are ammeters of negligible resistance. With switch S closed, the current passing through the 8 Ω resistor is 0,5 A, and resistor R delivers 12 W of power. 6.2 Calculate: 6.2.1 The reading on ammeter A₁ 6.2.2 The reading on ammeter A₂ 6.2.3 The emf of the battery (ε).

QUESTION 1. 1.1 Two forces, F₁ and F₂, act simultaneously at a point. The resultant force is 17 N when they act in the same direction, and 5 N when they act in opposite directions. The magnitude of the two forces are: A. 14 N and 3 N B. 11 N and 6 N C. 5 N and 12 N D. 10 N and 7 N. 1.2 A person stands on a bathroom scale that is calibrated in newton, in a stationary elevator. The reading on the bathroom scale is W. The elevator now moves downward with a constant acceleration of ¼g, where g is the gravitational acceleration on Earth. What will the reading on the bathroom scale now be? A. ¼W B. ¾W C. W D. 5/4 W. 1.3 Two objects of masses 2m and m are arranged as shown in the diagram below. Which of the following changes will result in the largest increase in the gravitational force the two objects exert on each other? A. Double the mass of each object. B. Double the larger mass and double the distance between their centres. C. Double the larger mass and halve the distance between their centres. D. Triple the smaller mass and halve the distance between their centres. 1.4 Two charges, +Q and −Q, are each placed a distance d from a negative charge −q. The charges, +Q and −Q, are located along lines that are perpendicular to each other, as shown in the diagram below. Which ONE of the following arrows CORRECTLY shows the direction of the net force acting on charge −q due to the presence of charges +Q and −Q? 1.5 The diagram below shows a magnet that is moved towards a solenoid. Which ONE of the following combinations are CORRECT? A. North, X to Y B. North, Y to X C. South, X to Y D. South, Y to X. 1.6 Which ONE of the following graphs best represents the relationship between the electrical power (P) dissipated by a resistor and the potential difference (V) across the resistor if the resistance of the resistor remains constant? 1.7 Which ONE of the following is the unit of measurement for the rate of flow of charge? A. Coulomb B. Ampere C. Volts D. Watts. QUESTION 2. Two forces act simultaneously on a small boat in a flat part of a river: the motor exerts a force of 1 200 N at an angle of 40° north of east; the river current exerts a force of 800 N in a northerly direction. The boat is at point O. 2.1 Define the term resultant vector. 2.2 Using an accurate scale drawing, determine the magnitude and direction of the resultant force acting on the boat. Use the scale 1 cm : 200 N.

QUESTION 6. A circular coil with 150 turns is placed in a uniform magnetic field of strength 0,5 T. The plane of the coil initially makes an angle of 40° with the magnetic field, as shown in Diagram 1 below. The coil is uniformly rotated in 0,2 seconds so that its plane is parallel to the magnetic field, as shown in Diagram 2 below. During this rotation, the induced emf in the coil is 0,43 V. 6.1 State Faraday's law of electromagnetic induction in words. 6.2 Calculate the change in magnetic flux during the rotation of the coil. 6.3 Determine the area of one turn of the circular coil. QUESTION 7. Three resistors and a light bulb are connected to a battery with an emf (ε) of 12 V and an unknown internal resistance (r) as shown in the diagram below. The ammeter and connecting wires have negligible resistance. The voltmeter reads 4,8 V when the switch is closed. 7.1 Define the term power in words. 7.2 Calculate the: 7.2.1 Effective resistance of the parallel combination 7.2.2 Reading on the ammeter.