Pg 179

Q1) Say whether the following attract or repel:a) two negative chargesb) a negative charge and a positive chargec) two positive charges

Q2) In an atom, what kind of charge is carried bya) Protons b) electrons c)neutrons?

Q3) What makes copper a better electrical conductor than polythene?

Q4) Why is it easy to charge polythene by rubbing, but not copper?

Q5) Name one non-metal that is a good conductor.

Q6) When someone pulls a plastic comb through their hair, the comb becomes negatively charged.

a) Which ends up with more electrons than normal, the comb or the hair?b) Why does the comb become negatively charged?

A1) a) Repel. b) Attract. c)Repel.A2) a)Positive (+) b)Negative (-) c) No chargeA3) Copper is a metal. Therefore, the electrons are free to flow. As the electrons are free to flow, they can carry the charges across the metal.A4) This is because the electrons in copper are free to flow & the electrons in polythene aren’t. So, the charges in polythene will flow but, the charges in polythene wouldn’t. Therefore, the polythene will easily get charged but the copper wouldn’t.A5) Carbon Metal.A6) a) The comb b} This is because when a comb is pulled through the hair, then there is a transfer of electrons. Electrons carry a negative charge & Protons carry a positive charge. So if the comb gains electrons, then it will have a net negative charge as there are more negative charges (in electrons) than positive charges (in protons).

Pg 181Questions:1} a) Give an example of where electrostatic charge might be a hazard. b} How can the build up of electrostatic charges be prevented2} How many microcoloumbs are present in one coulomb?3} On the right, a charged rod is held close to a metal can. The can is an insulated stand.a) Where will the induced charges on the can be?b) Why is the can attracted to the rod even though the net(overall) charge on the can is zero?c) If you touch the can with your finger, electrons flow through it. In which direction is the flow?d) What type of charge is left on the can after it has been touched?

Answers:1} a) After planes fly, there may be a build up of a charge as there might be a transfer of electrons between the clouds and the plane. So, these charges will escape during fuelling in the form of a spark which could cause an explosion.b) The build up of electrostatic charges can be prevented by earthing. Earthing is the discharge of charges.2} 1 coulomb=1/10-6 microcoloumbs.3} a) On the two sides(left & right) of the can.b) This is because the negative charges in the can are repelled from the left side (close to the rod) as, like charges repel. This leaves positive charges on the left side and so as like charges attract, the left side of the can is attracted to the rod.c) The electrons flow from the can through the finger and into the earth. This is because, the place where the finger will touch will be mainly negative charges and so, the electrons are in excess in this area and so it will flow from the can to the earth.d) A net positive charge is left.

Pg 183 Questions:1} Convert these currents into amperes: a)500 mA b)2500 mA2} Convert these currents into milliamperes: a) 2.0A b) 0.1A3} c) Two bulbs are connected in series. One ammeter shows 0.5A. What does the other one show?d) What bulb will go out if the switch contacts are moved apart? Give a reason for your answer.4} What charge is delivered ifa) a current of 10A flows for 5 secondsb) a current of 250 mA flows for 40 seconds

Answers:1} a) 1A = 100mA. So, 500mA=500/1000=0.5Ab) 2500mA= 2500/1000=2A.

2} a) 2A=2*1000=2000mAb) 0.1A=0.1*1000=100mA

3} c) 0.5A also as current is equal in series connectiond) Bulb B

4} a) Q=I*TQ=10*5=50Cb} 250mA=250/1000=0.250AQ=0.25*40Q=40C

Pg 185Question:1} In what unit is each of these measured?a) PD b)EMF c) Charge d) Current e) Energy

2} In the circuit on the right, the two bulbs are of different sizes & brightnesses.a) What type of meter is X?b) What type of meter is Y?c) What is the reading on meter Y?d) How much potential energy does each coulomb have as it leaves the battery?e) How much potential energy is lost by each coulomb passing through bulb A?f) How much charge passes through A every second?g) How much energy is radiated from A every second?

Answers:1} a) volt b) volt c) Coulomb d) joules2} a) Ammeterb) Voltmeterc) 8Vd) 12 joules of potential energy are given to each coulomb of charge.e) 4 joules of energy is lost.f) g)

Pg 187Questions:1} When a kettle is plugged into the 230V mains, the current through its element is 10A.

a) What is the resistance of its element?b) Why does the element need to have resistance?

2} In the diagram at the top of this page, a variable resistor is controlling the brightness of a bulb. What happens if the slide control is moved to the left? Give a reason for your answer.

3} Which of the components in the photographs above has each of these properties?a) A high resistance in the dark but a low resistance in the light.b) A resistance that falls sharply when the temperature rises.c} A very low resistance in one direction, but an extremely high resistance in the other.

Answers:1) a} R=Voltage/Current

=230/10=23 ohmsb} This is because there is a heating effect whenever a current flows through a resistance

2) If the slide control is moved to the left, the resistance will decrease. This is because the length if resistance in a wire is decreased.

3) a) Light dependant Resistor (LDR)b} Thermistorc) Diode

Pg 189Questions:1) The graph lines A and B on the right are for two different conductors. Which

conductor has the highest resistance?2) Using the left-hand graph above, calculate the resistance of the tungsten

filament when its temperature is a) 1500oC b) 3000oC3) In the right-hand graph above, does the diode have its highest resistance in

the forward direction or the reverse? Explain your answer.4) A resistor has a steady resistance of 8 ohms.

a) If the current through the resistor is 2A, what is the PD across it?b) What PD is needed to produce a current of 4A?c) If the PD falls to 6V, what is the current?

Answers:1) Graph B has the highest resistance.2) A) R=V/I. So, r=2/1=1ohm.

B) R=12/3=4ohms3) It has highest resistance reverse. This is because when it is reverse, there is no current flowing through it which means it has very high resistance. However, when it is forward, after 0.6V then the current can pass through which means that it has less resistance.4) A) V=I*RV=2*8=16VB) V=I*RV=4*8=32VC) I=V/RI=6/8I=3/4 A

Pg 191Questions:1) When one of the lights on a Christmas tree breaks, the others go out as well.

What does this tell you about the way the lights are connected?2) Give two advantages of connecting bulbs to a battery in parallel.3) Redraw either of the circuits on the left so that it has a single switch which

turns both bulbs on and off together.4) This question is about the circuit on the right:

a) The readings on two of the ammeters are shown. What are the readings on ammeters X & Y?

b) If the PD across the battery is 6V, what is the PD across each of the bulbs? (Note: you can neglect the PD across an ammeter.)

Answers:1) The lights are connected in series.2) 1) The voltage will be equal and not shared across the batteries.

2} If one bulb goes off, only the bulbs in the same series will go off.3)

4} a) Y=2A, X=2A b) 6V across both bulbs.