A circuit consists of a battery, a voltmeter and five fixed resistors, as shown. The voltmeter reading is zero. What is the resistance of resistor R?

• 1.1 Ohms

• 2.1 Ohms

• 4.0 Ohms

• 8.0 Ohms

The sum of the currents entering a junction in an electrical circuit is always equal to the sum of the currents leaving the junction.

• It is a consequence of the conservation of charge.
• It is a consequence of the conservation of electromotive force.
• It is a consequence of the conservation of energy.
• It is a consequence of the conservation of potential difference.

None

• P/Wd
• Wv/P
• Wd/P
• Pv/W

A known tensile force acts on a metal wire. The wire does not exceed its limit of proportionality. Which two measurements enable the strain of the wire to be calculated?

• The unstretched length of the wire and the cross-sectional area of the wire
• the unstretch length of the wire and the extension of the wire
• the young modulus of the metal and unstretched lenght if the wire

A wire has a resistance of 30 W. A second wire is made from the same material, has the same mass and is three times as long as the first wire. What is the resistance of the second wire?

• 10ohms
• 30ohms
• 90ohms
• 270ohm

What is the definition of the potential difference (p.d.) across a component?

• the electrical power supplied to the component
• the energy transferred to the component per unit charge
• the product of the current in the component and its resistance
• the voltage across the component

A cell with constant electromotive force (e.m.f.) is connected across a fixed resistor. Over time, the internal resistance of the cell increases. Which change occurs as the internal resistance of the cell increases?

• a decrease in the charge of each charge carrier
• a decrease in the potential difference measured across the cell
• an increase in the energy dissipated per unit time in the fixed resistor
• an increase in the number of charge carriers leaving the cell per unit time

The intensity of light incident on a light-dependent resistor (LDR) is increased. The temperature of a thermistor is increased. In each case, the current in the component is maintained at a constant value. What happens to the potential difference across each component?

• LDR increases; thermistors increases
• LDR increases; thermistor decreases
• LDR decreases; thermistor increases
• LDR decreases; thermistor decreases

An iron wire has length 8.0 m and diameter 0.50 mm. The wire has resistance R. A second iron wire has length 2.0 m and diameter 1.0 mm. What is the resistance of the second wire?

• R/16
• R/8
• R/2
• R

A resistor has resistance R. When the potential difference (p.d.) across the resistor is V, the current in the resistor is I. The power dissipated in the resistor is P. Work W is done when charge Q flows through the resistor. What is not a valid relationship between these variables?

• I = P/V
• Q = W/V
• R = P/I^2
• R = V/P