Unit 2

Question 1

What effect does a higher capacitance have on the rate of charge/discharge

Answer 1

• increases time taken to charge

- longer for charge to build up on plates

Question 2

Explain forward bias in terms of bands

Answer 2

• voltage from supply lowers energy of conduction band
• raises energy of valence band
• less work is done

Question 3

What is e.m.f

Answer 3

The work done in moving each coulomb of charge in the circuit

Question 4

What is a.c

Answer 4

Alternating current

• negative charges move back and forth
• changes direction

Question 5

What happens if the timebase is halved

Answer 5

There will be have as many waves as before on the screen

Question 6

When is a Wheatstone bridge circuit balanced

Answer 6

When the voltmeter reads zero

Question 7

When is a Wheatstone bridge circuit out-of-balance

Answer 7

When the voltmeter doesn’t read zero

Question 8

What band is full in an insulator

Answer 8

Valance band (lower band)

Question 9

How can a diode be reversed biased

Answer 9

N-type connected to positive terminals. No conduction occurs

Question 10

How can a diode be forward biased

Answer 10

N-type connected to negative terminals. Conduction occurs

Question 11

What is added to give a p-type

Answer 11

Indium

Question 12

What is added to give a n-type

Answer 12

Arsenic

Question 13

What is a semiconductor

Answer 13

Insulating material that has been doped with an impurity to increase its conductivity

Question 14

What effect will heating a semiconductor have

Answer 14

Resistance will decrease

Question 15

What effect does a higher resistance have on the rate of charge/discharge

Answer 15

• increases time taken to charge
• decreases current
• decreases rate at which charges flow onto capacitor plates

Question 16

Draw a graph of current against time for charging/discharging

Answer 16

(See notes for graph)

Question 17

If resistance is increased across a resistor, what happens to the voltage and the current in the resistor

Answer 17

• voltage increases

- current decreases

Question 18

How would internal resistance and e.m.f be found from a voltage/current graph

Answer 18

Gradient = -r
Y-intercept = e.m.f

Question 19

How would internal resistance and e.m.f be found from a resistance current graph

Answer 19

Gradient = e.m.f
Y-intercept = -r

Question 20

What is d.c

Answer 20

Direct current

• flows in one direction
• negative to positive

Question 21

When can e.m.f be measured

Answer 21

When there is no current flowing

Question 22

What is a capacitor

Answer 22

An electrical component that can store charge and therefore energy

Question 23

What is capacitance

Answer 23

The amount of charge stored per unit of potential difference

Question 24

What is internal resistance

Answer 24

The resistance of electrical source due to moving charges

Question 25

Explain reverse bias in terms of bands

Answer 25

- voltage of supply will raise energy of conduction band - lower energy of valence band - more work is done

Question 26

How would the internal resistance of the cell be found

Answer 26

Voltmeter connected across the terminals of the cell

Question 27

What happens when a capacitor charges

Answer 27

- voltage will increase until it equals supply voltage - current starts from maximum and decreases from zero - due to voltage increasing to supply

Question 28

Draw a graph of p.d against time for charging/discharging across resistors

Answer 28

(see notes for graph)

Question 29

Draw a graph of potential difference against time for charging/discharging a capacitor

Answer 29

(See notes for graph)

Question 30

How would you calculate Vreading on voltmeter on an out-of-balanced Wheatstone circuit

Answer 30

- V1 = R1/R1+R2 x Vs - V3 = R3/R3+R4 x Vs - Vreading = V1 - V3

Question 31

What is lost volts

Answer 31

The potential difference used by the internal resistance

Question 32

What is current

Answer 32

The amount of charge flowing per second

Question 33

How is voltage found from a line on an oscilloscope

Answer 33

V = number of vertical divisions for amplitude x y-gain

Question 34

How is the period of a wave calculated from an oscilloscope reading

Answer 34

T = number of horizontal divisions for one wavelength x timebase setting

Question 35

Why might components get damaged

Answer 35

If the peak supply voltage is greater than the average voltage

Question 36

Describe the difference for current in a series and parallel circuit

Answer 36

Series - equal | Parallel - current total = sum of current components

Question 37

Describe the difference in voltage for a series and parallel circuit

Answer 37

Series - vtotal = v1 = v2 + v3 | Parallel - voltage equal

Question 38

What is resistance

Answer 38

The opposition to electrical current

Question 39

When is the resistance largest in a circuit

Answer 39

When connected in series

Question 40

What is power

Answer 40

The amount of energy transferred per second

Question 41

What is internal resistance

Answer 41

Resistance of the electrical source (battery) due to moving charges

Question 42

What is a p-n junction diode

Answer 42

An electrical component that is made of two types of semiconductor

Question 43

What type of charges does the n-type lose

Answer 43

Negative charge carriers

Question 44

What creates the depletion layer

Answer 44

The p-type losing positive charge carriers and the n-type losing negative charge carriers

Question 45

In what direction (relating to the circuit symbol for a p-n diode) can the electrons flow

Answer 45

Against the direction of the arrow

Question 46

What band is partially filled in the n-type semiconductor

Answer 46

Conduction band