Chapter 4 Electric Circuits

Question 1

What is electric current

Answer 1

The flow of electrical charge

Question 2

What is a cell (description + description of photo)

Answer 2

Provides the ‘push’ for electrons in a circuit
- + and - with two lines of separate length

Question 3

What is an ammeter (description + description of photo)

Answer 3

Used to measure current
-circle with A

Question 4

What is a voltmeter (description + description of photo)

Answer 4

Used to measure the potential difference (voltage)
- circle with V

Question 5

What’s a lamp (description + description of photo)

Answer 5

Emits light when current passes through it
-circle with cross

Question 6

Whats a ldr (description + description of photo)

Answer 6

Light dependant resistor
- circle with rectangle and 2 arrows top left

Question 7

What’s a fuse (description + description of photo)

Answer 7

Melts + breaks circuit if current is too high
-rectangle with line going through it

Question 8

What’s a resistor (description + description of photo)

Answer 8

Limits current in a circuit
-rectangle

Question 9

What’s a LED

Answer 9

Emits light when current passes through it
- circle with line going through it with play button with two arrows top right from angle

Question 10

What’s a switch (description + description of photo)

Answer 10

Enables current in a circuit to be switched in or off
-one line,small circle line up - gap - small circle,small line ( open) - full line with two small circles (closed)

Question 11

What’s a thermistor (description + description of photo)

Answer 11

Temperature dependant resistor
-rectangle with line from bottom right flat then change angle to top right

Question 12

What’s a variable resistor (description + description of photo)

Answer 12

Allows current to be varied
-Rectangle with diagonal line from bottom left to top right

Question 13

What sub atomic particle carry’s electric charge and where do they transfer energy

Answer 13

Millions of electrons - from the power source to the components in the circuit.

Question 14

How to measure electrical current

Answer 14

I = Q / T

Current (amps) = charge (coulomb) / time (seconds)

Question 15

What is potential difference

Answer 15

P.d. is the amount of work done (energy transferred) by each coulomb of charge that passes through the circuit between two points.

Question 16

How to measure potential difference

Answer 16

V = E / Q

Potential difference (voltage) = energy (j) / charge (coulombs)

Question 17

What is resistance

Answer 17

the opposistion to the flow of charge. Resistance is measured in a unit called ohms

Question 18

4 factors that affect the resistance in a wire

Answer 18

• Length of wire
• Heat/temparature
• Type of material/Conductivity
• Diameter/cross sectional area of wire

Question 19

What is ohms law

Answer 19

The current through a resistor at constant temperature is directly proportional to the Potential difference across the resistor.

Question 20

How to measure potential difference with resistance

Answer 20

V = I x R

Potential difference (voltage) = current (Amps) X resistance (ohms)

Question 21

How does current vary with voltage

Answer 21

As potential difference (voltage) increases current increases - directly proportional

Question 22

Method of investigating Investigate whether a resistor, lamp and diode follow Ohm’s Law

Answer 22

1. Collect equipment listed.
2. Set up circuit as shown.
3. Insert the component to be tested into the circuit.
4. Set the variable resistor to maximum and turn on the switch
5. Record the current on the ammeter and the voltage on the voltmeter
6. Move the slider on the variable resistor to four more positions and repeat
   step 5.
7. Repeat the experiment with other components

Equipment - • Cell
• Variable resistor
• Wires
• Ammeter
• Voltmeter
• Switch
• Resistor
• Filament Lamp
• Diode

Question 23

How/are different components are proportional (resistor,filament lamp,diode)

Answer 23

P.d across resistor is directly proportional to the current in the resistor.The resistance of the resistor is constant

The potential difference across a filament lamp is not directly proportional to the current through resistor
A filament lamp does not obey ohms law and so can be described as a non - ohmic component. The resistance of a filament lamp is not a constant

The current is not directly proportional to the potential difference. The resistance changes as the current changes. A diode is a non ohmic conductor

Question 24

I-V characteristics Rp method

Answer 24

1. Set up the circuit as shown with the fixed resistor
2. Vary the voltage across the component by changing the resistance of the variable resistor, using a wide
   range of voltages (between 8-10 readings). Check the appropriate voltage reading on the voltmeter
3. For each voltage, record the value of the current from the ammeter 3 times and calculate the average
   current
4. Increase the voltage further in steps of 0.5 V and repeat steps 2 and 3
5. Make sure to switch off the circuit in between readings to prevent heating of the component and wires
6. Reverse the terminals of the power supply and take readings for the negative voltage (and therefore
   negative current)
7. Plot a graph of average current against voltage (an I–V graph) for each component

Question 25

What's a series circuit

Answer 25

when all the electrical components are wired one after another.

Question 26

Circuit rules in circuit series for current,pd and resistance

Answer 26

Current - same all over Pd - shared relative to the resistance Resistance - sum of resistance of component

Question 27

What is a parallel circuit

Answer 27

Circuit which has two loops

Question 28

Circuit rules for parallel circuit

Answer 28

Current - The total current through the whole circuit is the sum of the currents through the separate branches Pd-For components in parallel, the potential difference across each component is the same. This is because the electrons from the power source either pass along one route or the other Resistance- Adding more resistors in parallel decreases the total resistance. As the total potential difference is the same across each resistor. So adding an extra resistor in parallel increases the total current entering the combination.