Electrical Measuring Instruments
Physics ⇒ Electricity and Magnetism
Electrical Measuring Instruments starts at 9 and continues till grade 12.
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See sample questions for grade 11
A moving coil galvanometer has a coil of 100 turns, area 2 cm², and is placed in a magnetic field of 0.2 T. If a current of 1 mA passes through it, what is the torque on the coil?
A student uses a voltmeter with a resistance of 10,000 Ω to measure the voltage across a resistor. If the resistor has a value of 100 Ω, will the voltmeter reading be accurate?
A voltmeter is connected across a resistor in a circuit. If the voltmeter has a low resistance, what effect does it have on the measurement?
A voltmeter is designed to measure up to 10 V. If you want to increase its range to 50 V, what should you do?
Describe the function of a shunt in an ammeter.
Describe the working principle of a moving coil galvanometer.
Explain why a galvanometer cannot be used directly to measure large currents.
Explain why a potentiometer is considered more accurate than a voltmeter for measuring emf.
Explain why an ammeter is always connected in series with the circuit element whose current is to be measured.
If a galvanometer has a resistance of 50 Ω and gives full-scale deflection at 1 mA, what value of shunt resistance is needed to convert it into an ammeter of range 10 A?
Name the instrument that can be used to detect the presence of a small current but cannot measure its exact value.
State the main difference between a moving coil galvanometer and a moving iron instrument.
A digital multimeter is set to measure resistance. If the test leads are not connected to any component, the display shows 'OL' (overload). What does this indicate about the circuit being measured?
A galvanometer has a resistance of 40 Ω and shows full-scale deflection for a current of 2 mA. What is the maximum voltage that can be measured if it is used as a voltmeter with a series resistance of 4,960 Ω?
A moving coil galvanometer has a resistance of 20 Ω and requires 0.5 mA for full-scale deflection. Calculate the value of the series resistance required to convert it into a voltmeter of range 10 V.
A potentiometer wire is 1 m long and has a resistance of 10 Ω. If a cell of emf 2 V and negligible internal resistance is connected across the wire, what is the potential gradient along the wire?
Explain why a moving iron instrument can be used for both AC and DC measurements, whereas a moving coil galvanometer cannot.
In a laboratory experiment, a student uses a potentiometer to compare the emf of two cells. The balancing length for cell A is 60 cm and for cell B is 40 cm. If the emf of cell A is 1.5 V, what is the emf of cell B?
State the main reason why a Wheatstone bridge is more sensitive when all four resistances are of the same order of magnitude.
