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Find the magnitude of the force on an electron that is travelling with velocity 2 x 10^4 ms^(-1) in the x direction through a uniform magnetic field of strength 2T in the y direction.

This question tells us we only need to consider the magnitude of the force, and since the magnetic field and electron's velocity are perpendicular, we can simply use the equation F = Bqv. We have B = 2 T , q...
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Answered by Sally H. • Physics tutor
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What is viscosity?

Viscosity is a measure of a fluid's resistance to flow . It describes the internal friction of a moving fluid. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of inter...
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Answered by Juan N. • Physics tutor
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A capacitor discharge circuit of time constant 45ms includes a capacitor and resistor. The capacitor has a capacitance of 18µF What is the resistance of the resistor?

This question is in one of the CIE Physics Pre-U sample papers, and if you know the definition of the time constant for a capacitor circuit (=RC), its very easy, however even if you didnt it canbe derived fa...
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Answered by Sam C. • Physics tutor
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What determines the acoustic impedance of a material and why is it useful in understanding ultrasound imaging?

Acoustic impedance is the density of a material multiplied by the speed of sound in the material. Knowing these two values allows use to calculate how much of the sound energy is reflected at an interface be...
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Answered by David A. • Physics tutor
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How is a piezoelectric crystal used to generate waves of ultrasound?

A piezoelectric crystal makes use of the peizoelectric effect . This is the production of a voltage when mechanical stress is applied across the material. This occurs only in materials when the unit cells wh...
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Answered by David A. • Physics tutor
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