ELECTROMAGNETISM

Question 12 SPM2005(a)State the transformation of energy correctly.(1)

Gravitational potential energy Kinetic energy electrical energy.

12(a)(ii)State four reasons and brief explaination correctly-Save cost by cutting loss of power through cable using high voltage transmission. It reduces the current flows through the cable.(1M)

-Ensure continuous supply of power as all power is fed into the national grid network(1M)

-Power station which are damaged or need to be serviced can be replaced by other power station in the grid system.(1M)

-Generation of electrical power can be controlled and adjusted according to the demand of the day. Some power station can be temporary stopped during the low demand at night. (1M)

12(b)Determine the number of turns in the primary and secondary coils for transformer P,Q and R. ( 5M)For transformer P(12V to 24V)Vp/Vs = Np/Ns12/24 = Np/Ns = Np/Ns (1M) Choose Np=500, Ns=1000 (1M)

For transformer Q(24V to 8V)Vp/Vs = Np/Ns24/8 = Np/Ns3/1 = Np/Ns(1M)Choose Np=1200, Ns=400 (1M)

For transformer R (24V to 6V)Vp/Vs = Np/Ns24/6 = Np/Ns4 = Np/NsChoose Np=500, Ns=120 (1M)

12(b)(ii)State the correct type of laminated iron core and reason.Type of transformer core used is laminated soft iron core.(1M)Can reduced eddy current induced in the laminated core. (1M)Reduced loss of power due to hysteresis.(1M)

12(b)(iii) State the correct type of material and justify.Aluminium.(1M) Less density, lighter , low electrical resistance and economical. (1M)

12(c)I = V/R = 24/30 (1M) (Correct substitution) = 0.8 A (1M) (Correct answer with units)

Power loss = I2R (1M) (Correct formula) = (0.8)230 (1M) (Correct substitution) = 19.2W (1M) (Correct answer with unit)

SPM FIZIK 2006 Q10State what is meant by magnetic field.(1) A region of space where a magnetic material experiences a magnetic force.(b) Compare each of the aspects correctly.The number of turns of the coil in Diagram 10.2 is higher than in Diagram 10.2 (1)The pattern of iron filings formed in Diagram 10.2 is denser than in Diagram 10.1The deflection of ammeter in Diagram 10.2 is bigger than in Diagram 10.1.

12(c)State the relationship correctly

The denser the pattern iron filings, the stronger is the strength of magnetic field.(1)The bigger the number of turns of the coil, the stronger the strength of the magnetic field. (1)

12(d)Give the correct explainationWhen current flows, a magnetic field is formed and the force is exerted to the wire as shown in the diagram below.(1)

PQRS

12(d)The direction of current in the copper strip PQ and RS is in the opposite direction.Thus the direction of magnetic field produced in between the wires is in the same direction.(1)The resultant magnetic field at the space in between the wires strips is stronger than the surrounding area.(1) Thus, the wire strips repel each other.(1)

12(e)(i) Give correct explaination.When current flows through the coil, magnetic field is formed around the coil.(1)The magnetic field formed by the flow of current interacts with the permanent magnetic field of the motor.(1)It produces a resultant catapult field as shown in diagram,(1) (Draw the diagram)Thus, a pair of equal and opposite forces is produced which rotate the amature.(1)

12(e)(ii) Suggest modification and explain.Connect a full-wave rectified circuit using four diodes and a capacitor .(1)To convert the a.c to d.c current circuit and smoothen the d.c current produced.(1)Replace the slip rings of the a.c motor with a split ring(commutator)(1)It reverses the direction of the current to ensure flows through the amature to ensure it rotates in one direction only.(1)Increase the number of turns of the coil of the ammature.(1)To produce stronger coupling force which can rotate the ammature faster.(1)

SPM2007 SECTION A Q7(a)(i) Name the type of transformer correctly.(1) Step-down transforemr

7(a)(ii)State a correct reason for using soft iron as the transformer core.(1)

Soft iron can be easily magnetised and demagnetised. Thus, it reduces power loss due to hysteresis.

7(b)Correct substitution.(1) Vs/Vp = Ns/Np 6/240 = Ns/1000Correct answer.(1) Ns = 250

7(c)(i)Correct substitution.(1) Power output = 0.75 x Power input = 0.75VpIp = 0.75 x 240 x 0.1Correct answer with units. = 18 W

7(c)(ii)Give a correct suggestion/modification to improve the efficiency of the transformer.(1) Use laminated iron core./Use low resistance wire./ Increase the diameter of the coil.

7(d)(i)State the reason correctly.(1) Transformer supplies alternating current(a.c) and the television circuit works with direct current(d.c) only.

7(d)(ii)Name the electrical component correctly.(1) Diode.Describe the connection correctly.(1) A diode is connected in series with the output circuit./ Four diodes are connected in a form of bridge rectifier.

SPM2008 SECTION Q4(a)(i) Name the correct component in box X (1) Step-down transformer.

(a)(ii) Explain why a.c is used correctly.(1) To create a changing/fluctuating magnetic field which link the primary coil to the secondary coil.

(a)(iii) State the correct physics concept.(1) Electromagnetic induction.

(b) Output power = 0.8VpIp 65 = 0.8x240Ip ( 1M for correct substitution) Ip = 0.34A (1M for correct answer with unit)

(c) Any two diodes in correct position.(1) All diodes connected in correct position(1)

SPM 2009 SECTION A Q7(a)(i) Name the correct rule.(1) Flemings left hand rule.

(a)(ii) Draw the correct pattern and direction of the resultant magnetic field.(1) Show the correct direction of the resultant force,F (1)

7(b)(i)Use curve shaped magnets.(1)Draw radial magnetic magnetic field.(1)Indicate the direction of the magnetic field.(1)

NS

7(b)(ii) State a correct reason of using curve shaped magnets.(1)To produce radial magnetic field so that a constant force,F, is produced on the coil of copper wire.

7(b)(iii)Suggest a suitable component to overcome parallex error.(1)Plane mirror strip placed below the pointer across the scale.Give correct explaination for the suggestion.(1)To help to position the eye directly above the scale when taking reading to avoid parallex error. This happens when the image of the pointer coincides with the pointer

SPM 2011 SECTION B Q10(a)(i) State the meaning of electromagnet correctly.(1)Tempopary magnet produced by the flow of current through a conductor.

10(a)(ii)Compare the number of turns of the coil correctly.(1) The number of turns of the coil in Diagram 10.2 is more than in Diagram 10.2.Compare the reading of the ammeter correctly.(1) The ammeter reading in Diagram 10.2 is higher than in Diagram 10.1.Compare the number of iron nails atteached to the electromagnet.(1) The number of iron nails attached to the electromagnet in Diagram 10.2 is bigger than in Diagram 10.3.

10(a)(ii)State the correct relationship between the ammeter reading and the number of iron nails attached to the electromagnet.(1) The higher the ammeter reading, the bigger the number iron nails attached to the electromagnet.State the correct deduction regarding the relationship between the electric current and the strength of the electromagnet.(1) The higher the current, the stronger the electromagnet.

10(b)(i)Give the correct explaination why soft iron core is used.(1) Can be easily magnetised and demagnetised, thus reduces loss of power.

10(b)(ii)Describe how the relay function as a relay switch.Give three distinct steps of operation.(3) When current, soft iron core is magnetised.(1) The iron amature is attracted to the soft iron core causing the pivot to pushed up the lower contact.(1)The secondary circuit is completed and the motor is switched on.(1)

10(c)Give at least five suitable suggestions and correspondig reasons to increase the loundness of the sound.(10).Increase the number of turns of the coil round the soft iron core.(1) Increase the strength of the electromagnet.(1)

10(c)Increase the size of the gong.(1) Can cause more vibaration due to bigger surface area. It will produce sound waves with higher amplitude. Lower elasticity of the spring steel strip.(1) To increase the hitting force.(1)U-shaped soft iron core.(1) Increase the strength of electromagnet.(1)Thick wire,(1) Low resistance to allow larger current flows.(1)