Unit 2.3: DC Circuits

Question 1

To measure current, how is the ammeter connected: in series or in parallel?

Answer 1

In series to avoid affecting the current and have negligible resistance

Question 2

Is the current the same or different across all points in parallel circuits?

Answer 2

Different-the value of the branches add up to the total current.

Question 3

Explain in terms of current, the conservation of charge

Answer 3

The sum of the currents entering a junction is equal to the currents
leaving the junction. This is due to the conservation of charge.

Question 4

How are the voltmeters connected to all circuits. In series or in parallel?

Answer 4

In parallel, across the component

Question 5

How is the conservation of energy involved when speaking about potential difference in a series circuit?

Answer 5

The sum of the p.d’s across components in a series circuit is equal to
the p.d. across the supply. This is a consequence of the conservation
of energy.

Question 6

What is the potential difference in a parallel circuit?

Answer 6

the p.d. across all components in parallel is the same.

Question 7

State the equation for total resistance in a series circuit.

Answer 7

Rt=R1+R2+R3+…

Question 8

State the equation for total resistance for a parallel circuit

Answer 8

1/Rt=1/R1 + 1/R2+..

Question 9

In a Parallel circuit. The total current input
is equal to the current
through each branch of
the circuit. This obeys what law?

Answer 9

Conservation of charge

Question 10

In a parallel circuit. The potential difference
across each component
is equal. This obeys what law?

Answer 10

The law of conservation of energy

Question 11

For a series circuit. The current is equal at every point in the circuit. This obeys the law of what?

Answer 11

Conservation of charge

Question 12

For a series circuit. The total potential difference input is equal to the sum of the potential differences across the
components. This obeys the law of what?

Answer 12

Conservation of energy

Question 13

When is a potential divider circuit used?

Answer 13

When a certain output potential
difference is required.

Question 14

State the potential divider equation

Answer 14

Vout=Vs x R2/R1 + R2

Question 15

What is an LDR?

Answer 15

A component that has a resistance that changes when light falls on it. As the
intensity of the light is increased so the
resistance of the LDR falls.

Question 16

What components are often used in potential divider circuit and what does this mean for the total resistance?

Answer 16

Thermistors and LDRs. The total resistance can change because the resistance of these components can change also

Question 17

What is a thermistor?

Answer 17

A temperature-sensitive resistor. The resistance decreases as temperature increases (usually)

Question 18

What is the definition for EMF?

Answer 18

The emf of a source is the energy converted from
some other form (e.g. chemical) to electrical potential energy per
coulomb of charge flowing through the source.

Question 19

State the equationS for EMF

Answer 19

V=E-Ir
V=energy transferred to the components per C of charge
E=Energy transferred to electrical energy in the cell per C of charge
r=Energy lost due to the internal resistance
Units:Volts

Question 20

What is the difference between EMF and p.d?

Answer 20

Emf is the total energy supplied to the circuit per unit charge, while p.d. is the electrical energy per unit charge converted to other energies by the components.

Question 21

If n cells are connected correctly, each with emf E and internal resistance r, the total emf will be what? and the total
internal resistance will be what?

Answer 21

Total EMF=nE
Rt=nr